NEWS he size and shape of the burner has a great deal to do with its efficiency in burning the pyrites there cannot I think be the slightest doubt. A pyrites-burner should have two chief qualificationsFirst, it should be large enough to take in the necessary charge of pyrites, so that they can be spread over the surface in a very thin layer; secondly, it should be small enough to enable the workman to get at all parts of it with as little trouble as possible, in order that the burning pyrites may be thoroughly opened out, thus allowing a free current of air to pass through, for the purpose of oxidising the burning sulphur as well as the metallic substances. In some works we find the burners built in a single row-charging the pyrites on the one side, and drawing the cinders on the other. I cannof see one single advantage this burner has to recommend its adoption, as it is very expensive to build, requires more space, and is very unhandy to work. I was told by a manufacturer, who has them in his works, that one great advantage they possess is that, by by putting the green ore in at one side and drawing the burnt ore on the other, there is no danger of the green ore getting mixed with the burnt ore and so being lost. By inaugurating a proper system of working this can be readily avoided. There is also another style of burner, which is made very large, and is charged with from 8 cwts. to 10 cwts. of pyrites. The advantage claimed for this burner is the great saving of labour connected with it: it requires to be charged once only in twenty-four hours. Its disadvantages, I think, outweigh the advantage it possesses. A pyrites, such as the first quality of Norwegian, may be burnt, but, if an ore is introduced into them that is at all liable to scar or slag, the large burner is very objectionable. The reason is the burning ore does not get pokered up often enough; it gets into lumps, and I have known a case in which the pyrites became a solid mass, necessitating the removal of the entire front of the burner before the working could be proceeded with. I do not think there could be anything better than the twelve hours system if the burners are not too heavily charged; the ore is pokered thoroughly every twelve hours, keeping it open and free from scars, thus causing it to burn very freely. The draught can also be regulated to burn the pyrites properly, and I have no doubt but, with the light charge and twelve hours, the ore will be found to be much better burnt than with the heavy charge and the twenty-four hours system. A great source of annoyance to manufacturers in making acid from pyrites is the accumulation of smalls. A number of plans have been tried to extract the sulphur, some of them with a fair amount of success, others proving quite a failure. The system in general use at present is a furnace, commonly called a blind- or close-furnace. It is heated by a coal fire placed at one end; the flame passing between two arches descends at the end farthest from the fire, passing under the bed of the furnace, thence to the chimney. The green dust is generally charged at the end farthest from the fire, being gradually moved up to the hottest end, where it is drawn, the reason of this being that the first equivalent of sulphur is readily driven off, while the second requires an intense heat to separate it from the iron. A great objection to this system is the quantity of coal used; in some cases as much as I ton of coal to 1 ton of dust being required to expel the sulphur. There is also the danger of the arch of the furnace getting cracked, the consequence being that the sulphurous acid, instead of passing into the chamber where it is wanted, passes into the chimney along with the heated air from the fire, thus giving a small production of sulphuric acid on the sulphur charged into the furnace. While at Messrs. Allhusen's I introduced a system of burning the small which has proved entirely satisfactory. Two cast-iron plates are introduced into the ordinary pyrites-burner, the heat from the burning pyrites igniting the dust and driving off the sulphur. In a number of years' working it has been found that on an average the burnt dust does not contain more than 1 per cent more sulphur than the burnt ore, which is very satisfactory. The burner is fitted with air-tight doors, and has a superficial area of about 17:25 feet. The metal plates on which the dust is burnt are each 1'8" x 5'2" and about 1" thick, resting on the brickwork at both ends and along one side. Along the front of the plate runs a flange about 3" high, for the purpose of preventing the dust getting in among the stones while being worked. The dust-door is made in two halves, in order that it may work easier on the hinges. When a plate requires to be renewed (which, on an average, is once in six months) the half of the door that is fast is taken off, the old plate removed, and the new one put in, the entire operation occupying only a few minutes. The dust is charged with a scoop from the front, and is raked over about four times every twelve hours. A hanger of malleable iron is introduced through the arch of the burner, passing under the front of the plate, thus keeping it from sinking (as it otherwise would do) when brought to a red heat. These burners are charged with 34 cwts. of pyrites per twelve hours and cwt. of dust. Each plate burns cwt. of dust per twenty-four hours, being charged alternately. Total charge per twenty-four hours per burner, 7 cwts. These burners give good results, and are very easily wrought and regulated. An objection has been sometimes raised to the admission of air to chambers through the dust-burners, the air taking up the chamber space, thus causing a loss in production. I think if the blind-furnaces are closely examined, the true cause of loss will be found in the dust having been badly burnt, or an escape of sulphurous acid through the openings in the brickwork. There is a greater danger, so far as good productions are concerned, in having too little oxygen in the chambers than in having even a very large excess. I have found over a number of years' working, with and without the dust-plates, that the produce of sulphuric acid is not at all affected by the extra quantity of air admitted while charging and working the dust. Amongst the ores most suitable for the manufacture of sulphuric acid are Mason's, Tharsis, Norwegian, and Belgian ores. The following is the composition of some of the ores which I have burnt : Composition. First Second I'20 I'IO 2:26 Sulphur Iron Copper Zinc .. Mason's. Belgian 45'60 38.52 nil 6:00 trace ΟΙΟ 0.28 Some of the ores also contain more silica than others. This I have found to be not at all injurious to the burning, provided the burners are kept at a proper heat. Most ores when burned at a high temperature "scar;" it has, however, been ascertained that the scar itself contains very little sulphur, but it is well to prevent this, as there is the danger of the scar enclosing pieces of raw ore, and also stopping the proper current of air through the burning pyrites. Sulphur, as is well known, on being burned in air is converted into sulphurous acid, a larger quantity of air being required for pyrites as compared with free sulphur, owing to the metals contained in pyrites absorbing oxygen to form oxides. The sulphurous acid passes into a flue in connection with the burners, in which are placed castiron vessels containing nitrate of soda and sulphuric acid, the heat of the gas decomposing the nitre, forming bisulphate of soda and nitric acid gas. The two gases react on each other, forming sulphuric acid and binoxide of nitrogen, the latter absorbing two equivalents of oxygen from the air, forming hyponitric acid, which is again acted on by the sulphurous acid, and thus acts as a carrier of oxygen from the air to the sulphuric acid. An excess of nitrous compounds or available oxygen must be always present, so that the whole of the sulphurous acid may be oxidised. A sample of nitrate of soda taken from the nitre-pots contained as follows: NaOSO3 Iron and alumina.. First.. Second Third.. Total.. .. 100'94 Various opinions exist as to the reaction going on in the chamber; in fact almost every chemist who has investigated the subject takes a different view. The most simple theory which many chemists hold is the following:3SO2+NO5=3SO3+NO2 NO2+20 NO4 2SO2+NO4=2SO3+NO2 The nitrous compounds are, as will be seen, ultimately reduced to NO2, after which it plays the part of carrier between the O of the air and the SO2. The agents, therefore, that we require in a chamber for the successful manufacture of sulphuric acid are sulphurous acid, hyponitric acid, air or oxygen, and steam. It will be seen that a very small quantity of nitrate of soda is required to convert the sulphurous acid into sulphuric acid; in fact, if no loss were sustained, the chamber being once filled with the nitrous compounds, no more would be required. This, however, is not the fact in practice, for when the chambers are working properly, and every precaution used to recover the excess of nitrous compounds required in the making of acid, a loss of from 3 per cent to 6 per cent of nitre is sustained. There are three sources of loss-First, the acid on the chamber-floor absorbing nitrous compounds; second, from that which escapes absorption in the absorbing-towers; and, third, from the nitric acid remaining in the sulphuric acid after it has been passed through the denitrating columns. (To be continued). 82.25 17'15 1'30 0'24 ON THE SULPHUR DEPOSITS OF KRISUVIK, ICELAND. It is somewhat to be regretted that no one amongst the numerous eminent men, men accustomed to experimental investigations and acute observers, who have since traversed this region, should have investigated the question of the origin of these hot springs and sulphur deposits from the point of view which was thus displayed by these careful and painstaking philosophers. The phlogistic theory being generally accepted in their day, and the chemistry of the earths and metals being in a very undeveloped state, we cannot now accept to its full extent the explanation they put forth of these phenomena; but the facts they disclose appear to me to be of the highest value, and to afford a clue which, if carefully followed, may lead to discoveries of much importance in the domain of volcanic energy. The conclusion they drew from their investigation is, that the hidden fires of Iceland dwell in the crust of the earth, and not in its interior; that the boiling springs and the mud cauldrons certainly do not derive their heat from the depths of our globe, but that the fire which nourishes them is to be found frequently at only a few feet below the surface in fermenting matters, which are deposited in certain strata. By their theory the gases from the more central parts of the earth penetrate these beds by subterranean channels, and so set up the chemical action, producing fermentation and heat, these channels also forming the means of intercommunication between the separate sites of activity, and equalising and transferring pressure. To return to their facts. They further observed that the heat is invariably found to be greatest in the blue and bluish-grey earth; that these earths almost always contain sulphuric acid; that they contain also sulphur, iron, alum, and gypsum; and lastly, that finely-divided particles of brass-coloured pyrites are visible throughout the whole of the beds when heat exists. Sulphuric acid is found in the hot beds above and below that which is the hottest, but this latter manifests no acidity that is sensible to the taste. Sulphuretted hydrogen is continually evolved from the Silver coins dropped into a hole made in these strata become rapidly clays containing the brass-coloured pyrites. reddened, and brass becomes quite black if held over it for a short time. Lastly, not only does the heat increase and diminish in various successive layers of the earth in the neighbourhood of the active springs, but the locality of the heat, as might be expected from their previous observations, travels very considerably in different years. Roberts. The solfatara of Krisuvik, with the mountains about it, is shown in the accompanying sketch by M. Eugène ancient crater, but, as we have already seen, it is not near It appears from afar to occupy the place of an the crater about the centre of the drawing, but at a considerable distance from the old volcanic centre, that the thermal springs and sulphurous exhalations have their present origin. Wherever they may have been previously, the springs stofer, on the right, originally composed of lava, the other, are now situated between two mountains; the one, BadVesturhals, on the left, of basaltic formation. Both by the action of the thermal springs are undergoing a process of disintegration and reconstruction. called, increase in extent day by day, by the addition to The kind of hills which form the solfataras, properly so the disintegrated rock of sulphnr, and of sulphurous and sulphuric acids. The yellow sulphur earth contains about four per cent of free sulphuric acid; sometimes a little free hydrochloric acid, and a variety of sulphates, as might be supposed. Treated with distilled water the filtered solution reddens litmus strongly; on addition of acetate of lead a flocculent precipitate is produced, which, when heated with carbon, disengages sulphurous acid. The sulphur is found in many different conditions, but for the most part in the same finely-divided, whitishyellow form in which it is precipitated from sulphuretted hydrogen solutions. Where it assumes other states, crystallised in tears on the surface of the rocks, or coagulated in veins, it is on account of its having undergone subsequent heating. Of its primary origin by the decomposition of sulphuretted hydrogen, there is in my opinion no doubt. Prof. Bunsen visited Krisuvik in 1845: his opinion is that sulphurous acid is evolved from the earth's interior, which, oxidised either at the surface by the atmosphere, or at subterranean depths by atmospheric oxygen dissolved in cold water, is converted into sulphuric acid. The sulphuric acid thus generated is diffused among the constiuents of the decomposed beds. This process represents the first stage of the fumerole action, which is manifested in the namar or solfatara of Krisuvik. Sulphur is now generally regarded as emanating from the stage of intermittent lethargy of a volcano, and the sulphides of iron, copper, arsenic, zinc, selenium, &c., fall in the same category as sulphur; they are secondary, not primary, formations. In the stage further off we have the host of sulphates produced by the oxidation of the sulphur into sulphuric acid, and its subsequent reaction on the metals and earths with which it becomes associated. The description of the Sicilian sulphur beds coincides so very exactly with that of the Icelandic mines, that one might pass very well for the other. D'Aubigny pictures nearly the whole of the central portion of Sicily as being occupied by a vast bed of blue clay or marl, in which are numerous and thick beds of gypsum and sulphur, and a combination of this mineral with iron and copper. The natural process by which they have been formed must, I think, be the same in each case. At Krisuvik copper has been found only in small quantities, but that is probably because it has not been sought for below the surface. Carbonate of copper, associated with sulphate of lime, is of frequent occurrence, and native copper has to a limited extent been discovered. A district in America, very similar in most of its characteristics, has recently been explored, The great hot-spring region of the sources of the Yellowstone and Missouri rivers, in the United States, has, on account of the wonderful natural phenomena there manifested, been set apart by the United States Congress as a great national park for all time. The whole of this district is covered with rocks of volcanic origin of comparatively modern date. At present there are no signs of direct volcanic action going on, but the secondary kind of action, resulting probably as at Krisuvik, from the disintegration and decomposition of beds of volcanic origin, is in full progress. Boiling springs, mud cauldrons, and geysers are found in all parts of the region, and the description given by Mr. V. Hayden, of the Yellowstone lake and its vicinity, in every respect coincides with those of the geysers, mud cauldrons, and hot springs of Iceland. In all cases there was found to be free access of water; free sulphur was widely dispersed, and the steam-jets were invariably accompanied by large quantities of sulphuretted hydrogen. The subterranean action in this country does not appear to have continued long enough to produce beds of sulphur and sulphur earths; but has, nevertheless, been of sufficiently long standing to build up geyser tubes of so great a length that the internal pressure has formed other vents, rather than lift the immense column of water above it. The water of the springs contains sulphuretted hydrogen, lime, soda, alumina, and a slight amount of magnesia; some of these are only occasionally at the boiling-point, and these, when the temperature is reduced below 150° F., deposit great quantities of the sesquioxide of iron, which lines the insides of the funnels, and covers the surface of the ground wherever the water flows. If the reaction consists in the decomposition of iron pyrites, and the sul phur is carried sufficiently far off to prevent its re-combination with the iron to form iron sulphate, the formation of the iron sesquioxide is fully accounted for. As a rule, the groups of hot springs are, as in Iceland, in the lower valleys, and either along the margins of streams, or nearly on a level with them. The grand area where they occur is within the drainage of the Yellowstone, where a space of 40 miles in length with an average width of 15 miles, is either at the present time, or has been in the past, occupied by hot springs. That the quantity of sulphuric acid here produced is very large is proved by the immense quantity of alum which is found, for the streams, the mud, the earth are thoroughly impregnated with it. The funnel-shaped craters from which the boiling mud is ejected, are so similar to those at Krisuvik that the figure on page 113 wil answer for both places. The circular rim varies from a few inches to several feet in diameter. Sometimes these are clustered close together, yet each one being separate and distinct from the others. The foregoing are the most prominent facts connected with the development of sulphur from the earth in the elementary state. The full explanation of all the phenomena accompanying it appears to me to be the key by which the great secret of volcanic energy may be ultimately unlocked. At present it appears to be doubtful whether the sulphur results from the decomposition of metallic sulphides, by heat and water combined, or by sulphuric acid formed by the oxidation of sulphurous acid. In the one case, the whole action is so far within our reach that it should not be an insurmountable difficulty to establish the point as to whether the whole action does not depend on the percolation of water into beds of pyrites surrounded by other beds which are non-conductors of heat. The other view, viz., that the sulphur proceeds as sulphurous acid from a lower depth, is, on account of the more complicated action required, far from being as satisfactory to my mind as the more simple supposition above. Until boring experiments have been made, conducted with great care, and to considerable depths, no positive conclusion can be arrived at. It is also an element in the question of much importance to discover whether the beds penetrated by the water are already heated, whether the water is heated before it reaches the sulphur-bearing strata (the clays containing pyrites), or whether both are not alike cold till they have been for some time in contact. Less than a quarter of a mile from the hot springs is a lake, Geslravatn, formed by the filling up of an extinct crater. This the inhabitants describe as being fathomless (Mr. Seymour, last year, found no bottom at five and twenty fathoms). The depth is, at any rate, very considerable. Although so close to a spot where the ground is, even at the surface, scorching to the feet, the water in this lake is ice-cold. Sir George Mackenzie also remarked a somewhat similar fact. On the side of the sulphur mountain, amidst the seething, steaming hills of almost burning earth, a spring of clear cold water was met with. To my mind these facts are most in accordance with the view that the action is local and self-dependent. The Krisuvik sulphur mines have been worked at various times, but want of proper roads, and ignorance of the proper method of extracting and refining the sulphur, have prevented their proper development. The Sicilian mines can be worked at a considerable profit, where, more than 390 feet below the surface, beds are met with containing only 15 per cent of sulphur. At Krisuvik, absolutely on the surface, clays are met with which contain from 15 to 90 per cent of sulphur. Under proper and careful supervision their future should be prosperous. Two German gentlemen, under the auspices of the Danish Government, worked these mines in the early part of the last century, and so much was exported to Copenhagen during the time the excavations were carried on, that a sufficiently large stock was laid up to serve the consumption of Denmark and Norway from 1729 to 1753. Horrebow describes the sulphur mines as being actively worked from 1722 to 1728, to the great advantage of the inhabitants, who reaped much profit from its extraction. By his account of their mode of prosecuting this enterprise, the sulphur does not appear to have been refined in the island, but exported in its crude state. The less active mines were chosen for cutting into. He says:-There is always a layer of barren earth upon the sulphur, which is of several colours, white, yellow, green, red, and blue. When this is removed the sulphur earth is discovered, and may be taken up with shovels. By digging 3 feet down the sulphur is found in proper order. They seldom dig deeper, because the place is generally too hot, and requires too much labour, also because sulphur may be had at an easier rate, and in greater plenty, in the proper places. Fourscore horses may be loaded in an hour's time, each horse carrying 250 lbs. weight. The best veins of sulphur are known by a kind of bank or rising in the ground, which is cracked in the middle. From hence a thick vapour issues, and a greater heat is felt than in any other part. These are the places they choose for digging, and after removing a layer or two of earth, they come to the sulphur, which they find best just under the rising of the ground, when it (the sulphur) looks just like sugar candy. The farther from the middle of the bank the more it crumbles, at last appearing as mere dust. But the middle of the bank is an entire hard lump, and is with difficulty broken through. The brimstone, when first taken out, is so hot that it can hardly be handled, but grows cooler by degrees. In two or three years these veins are again filled with sulphur. The death of the person at Copenhagen who had the sole and exclusive privilege of exporting sulphur from Iceland put an end to what had promised to be a very thriving industry. The inhabitants continued to collect the sulphur-earth for some time after its exportation had ceased; and many of them lost considerably by it, large quantities having been gathered which they were never able to dispose of. According to Dr. Perkins, the sulphur mines were again worked by the Danish Government for fifteen years, but the method of purifying adopted was very imperfect. The sulphur-earth was heated in iron boilers, and, when the sulphur was melted, fish oil was added, and the whole mass stirred up. On allowing the mixture to stand for a time, the earthy matter formed a soap on the top of the molten mass; this being removed, tolerably pure sulphur remained behind. In 1832, these mines were visited by K. von Nidda, the celebrated geologist, by whose advice a Danish merchant, named Kruntynon, purchased them. He only worked them for a short period. The sulphur-earth was collected without much regard being paid to the relative richness of the beds. It was taken on the backs of horses to Havnafiord, and thence shipped to Copenhagen. The cost of transport brought the sulphur to too high a price to render the undertaking successful. In 1857, political matters caused the attention of Her Majesty's Government to be directed to finding a new source of sulphur supply. Commander J. E. Commerell, of Her Majesty's ship Snake, was sent to Iceland by the Lords Commissioners of the Admiralty, to visit and report upon the capabilities of the mines of Krisuvik and Husavik. He found that the nearest safe port to the Krisuvik beds was Havnafiord; this port is 14 miles from the sulphur-beds by the present roads, and 9 miles from Reikjavik. The harbour is well sheltered, with good anchorage of 7 or 8 fathoms three cables length from the beach; it at present enjoys as much traffic as Reikjavik. The road from Krisuvik might be much shortened, and a tramway might also be laid down. During the past year a survey has been made, and plans drawn, for a railway or tramway to Havnafiord. The actual extent of the sulphur-beds it is quite impossible to calculate; forty-seven have been already discovered. The deposit of sulphur Commander Commerell personally saw he describes as amounting to many thousands of tons, and, all the mines being in what is called a "living" state, the sulphur taken away is reproduced in two or three years. He considers that sulphur in a pure state could be shipped at Havnafiord for £1 per ton. The sulphur at Myvatn, though great in quantity, is, he considers, at too great a distance from a port of embarkation to permit its extraction being carried on with any chance of competing with that from the Krisuvik mines. No further steps were taken in the matter by the British Government, the political complications which led to the expedition having been removed; but the attention of English merchants having been drawn to these rich deposits by the highly favourable character of Commander Commerell's remarks, renewed attempts are being made to render commercially available the immense sulphur-producing power which the Krisuvik solfataras undoubtedly possess. To some of these gentlemen I am greatly indebted for much valuable information, put at my disposal for the purposes of this paper, and, amongst them, I have specially to tender my thanks to Mr. Ramsdale and Messrs. Thorne, of Gracechurch Street, and particularly for the use of numerous and carefully-selected samples of the sulphur-earths which were freely placed at my disposal. These samples I hope to make the subject of a future paper. Since writing the foregoing paper, I mentioned, in the course of conversation with Sir Henry Holland, the conclusions which are derived from the examination of all the trustworthy facts relating to the sulphur deposits. This led him to examine entries in his unpublished diary, made at Krisuvik in 1810. The theory which he then conceived so thoroughly agrees with all that has been learnt respecting the phenomena in question, that I, with his kind permission, print an extract from his note-book : "The theory of these sulphurous springs (if springs they may be termed) at Krisuvik is an interesting object of inquiry. They are situated in a country decidedly of volcanic origin. The high ground on which they appear is composed principally of the conglomate or volcanic tufa, which has before been noticed. The source of the heat which can generate permanently so enormous a quantity of steam must, doubtless, reside below this rock; whether it be the same which produces the volcanic phenomena may be doubted, at least if the Wernerian theory of volcanoes be admitted. It certainly seems most probable that the appearances depend upon the action of water on vast beds of pyrites. The heat produced by this action is sufficient to raise an additional quantity of water in the form of steam, which makes its way to the surface, and is there emitted through the different clefts in the rocks. The sulphates of lime and alumina, appearing upon the surface, are doubtless produced, in process of time, by these operations. In corroboration of this view it may be observed that the quantity of steam issuing from the springs at Krisuvik is always greater after a long continuance of wet weather, and that whenever earthquakes occur on this spot it is during the prevalence of weather of this kind." The learned, and now aged, author expressed the highest gratification that the views which he formed at twenty-two years of age should possess so much value so many years after. During the reading of the paper Mr. Vincent illustrated his subject by several experiments, showing how the deposition of sulphur might have been effected. He also showed a spectrum obtained by burning some of the sulphur-earth, and it appeared that the thallium line became visible in the spectrum. Specimens of the various sulphur-yielding earths from Iceland were exhibited, and Dr. Clement Le Neve Foster showed samples from the Italian sulphur districts. PROCEEDINGS OF SOCIETIES. CHEMICAL SOCIETY. Dr. GLADSTONE, F.R.S., Vice-President, in the Chair. AFTER the minutes of the previous meeting had been read and confirmed, and the donations to the Society announced, the names of Messrs. E. H. Fison, Charles Thomas Kingzett, Alonzo J. Rider, William Andrew Prout, B.A., Roland Finch, William Morgan, Ph.D., and Henry Richardson, were read for the first time. For the third time-Messrs. George Ainsworth, Alexander Bottle, Richard Joseph Deeley, and James Walter Montgomery, who were then ballotted for and duly elected. The first paper, "On the Action of Hydrochloric Acid on Codeine," was then read by the author, Dr. C. R. A. WRIGHT, who, after referring to a former paper, containing an account of the action of hydrochloric acid on morphine, stated that codeine, treated with hydrochloric acid at 100° for 2 hours, gave a mixture of two bases, C+3HC and C+4HCl-2H2O, where C stands for C36H42N2O6. When the action was continued for a longer time, methyl chloride was evolved, and a mixture of two isomeric bases obtained, intermediate in composition between morphine and "apomorphine "-namely, M2-2H2O and M4-4H2O respectively, where M equals C34H36N2O5. With hydrobromic acid the first action was similar to that of hydrochloric acid, but its continued action gave rise to products which are not identical with those formed by means of hydrochloric acid, whether at 100° or at a higher temperature. An extensive table of the derivatives of codeine obtained up to this time accom panied the memoir. After the Chairman had expressed the thanks of the Society to Dr. Wright for his valuable and laborious researches on this subject, a paper "On New Processes for Mercury Estimation, and some Observations on Mercury Salts," by J. B. HANNAY, was read by the Secretary. The author, finding the ordinary processes for the determination of mercury either very tedious or deficient in accuracy, has devised two new ones which are free from these objections. The first, which is a volumetric method, depends upon the fact that potassium cyanide dissolves the precipitate produced by ammonia in a solution of mercury chloride. A few drops of ammonia are first added to the solution containing the mercury in the state of chloride, and then a standard solution of potassium cyanide until the turbidity produced by the ammonia disappears. If arsenic, copper, &c., be present, the solution should be precipitated by sulphuretted hydrogen, the arsenic, &c., separated by sulphide of ammonium, and the mercury sulphide dissolved in aqua regia. The other method consists in decomposing the mercury, in solution as sulphate, by the electric current in a platinum basin, the mercury being deposited on the basin in the metallic state and weighed as such. The author has also made several experiments on mercury salts, and finds that hydrochloric acid completely decomposes mercury sulphate, and that mercury chloride can even be boiled with concentrated sulphuric acid without suffering decomposition. Mr. F. FIELD remarked that, in separating the arsenic and antimony, potassium sulphide must not be used, as mercury sulphide was comparatively soluble in it. The next paper, "On a Method of Estimating Nitric Acid," by T. E. THORPE, F.R.S.E., was also read by the Secretary. The author finds that the copper-zinc "couple" of Messrs. Gladstone and Tribe completely decomposes nitrates with formation of ammonia, which can then be estimated as platinochloride, or, if the amount be but small, by Nessler's test; particular care, however, is required with ammonium nitrate, the strength of the solutions employed considerably affecting the result. The author believes that this process, applied to the determination of nitrates in potable waters, possesses considerable advantages over the ordinary method-namely, by avoiding the introduction of nitrates in the potash or soda employed, and the frothing of the strongly alkaline solution when distilled. The author also employs the couple" for the reduction of chlorates and iodates: it seems to have no action on urea. Dr. GLADSTONE said he had listened to the paper with great interest, and would welcome every labourer in the extensive field opened up by the use of the copper-zinc couple, since it was of great importance that we should know what substances were decomposed by it and what were not. Mr. W. THORP said he was much pleased with the paper, and had no doubt the method would be valuable in determining nitrates when they were present in tolerably |