RAY: THE NITRITES OF MERCURY, ETC. 337 XXXIK-The itTitrites of Memzcy cmcl the Varying Conditions uiadey which they cwe formed. By P. C. RAY, D.Sc. (Edin.). Hemu~ous Nit~ite," Hg,(NO,),. IN an earlier paper 9 on the preparation of the above salt, I said that 66yellow nitric acid of sp. gr. 1.410 is diluted with water in the proportion of 1 t o 3 ; a large excess of mercury is at once poured into the liquid, the heat of solution of the acid in water helps to start the reaction." This has since been repeated several times, and I have found that colour- lessnitric acid acts just as well, and that it is better to dilute it in the proportion of 1 to 4 ; in other words, dilute nitric acid containing 13 to 14 per cent. N,O, seems to be most favourable for tbe growth of the yellow, thin needles and prisms.For the results of analyses, see A I, 11, Table, p. 345. Nethod of Astcclgsis. Estinmtion of Mewury.--The mercury which separates out on gently heating the salt with water has been termed " free " mercury ; that contained in the clear solution in the rnemuvous state was thrown down as chloride by means of sodium chloride, and that existing in the filtrate in the mercuric form was estimated as sulphide. For details, see Zoc. cit., p. 267. Sometimes the free mercury comes out too low ; this is due chiefly to imperfect coagulation of the grey powder and loss by volatilisation. As a further check, some of the salt was dissolved in the minimum amount of strong nitric acid, sodium chloride was added t o the solu- tion, and the precipitated calomel was redissolved in aqua regia, and the total mercury precipitated as snlphide. For result of this analysis and the formula, &c., see A 111, Table, p. 345.I n the memoir referred to above, the mercury in the mercuric salt was generally thrown down as calomel by the addition of phosphorous acid; this method invariably gave too low results, in fact 30.7 was * Compare Divers and Haga, Trans., 1887, 41, p. 49. t Zeit. anorg. Chem., 1896, 12, 365, (from Journal Asiatic Society Bengal, 1896, lxv., ii, No. 1).338 R ~ ~ Y : THE NITRITES OF MERCURY AND THE VARYING taken as the mean percentage of mercury both in the " free " state as also in the mercuric salt ; in only one instance was the mercuric mercury estimated as sulphide, and this gave 31.33 as the percentage (Zoc.cit.). I naturally gave preference to the number 30.7, and mas thus misled into assigning the formula Hg,(NO,), + H,O to the salt. I have, how- ever, since then succeeded in preparing a hydrated salt of this formula, which will be described later on. Estinmtion of the iJTits.ogen.-As stated in the first paper, the nitrogen was estimated by the Crum-Frankland method. Determinations of nitrogen by the direct method, however, seemed highly desirable, especially as the various basic nitrites and nitrates to be subsequently described are but sparingly soluble in water, and are only partially decomposed on treatment with an alkali; conse- quently, the total nitrogen cannot be obtained in the soluble form. The method employed was that of Dumas, somewhat simplified.The salt was placed in a porcelain boat in a combustion tube and the whole length of the tube between the boat and the delivery tube was closely packed with bright copper foil, well-dried magnesite being used for the supply of carbonic anhydride. This method bad the additional advan- tage that the various stages of decomposition of tho salts could be watched, and also that it was easy to see whether water was given OB from them." For analytical data, see A 11, Table, p. 345. Foi*mation of the firitrite us Dependent o n the 8ts.ength of the Acid. A. Nitvie acid (1 : 4)-It has already been pointed out that the acid (sp. gr. 1.41) diluted in the proportion of 1 to 4 of water favours the growth of the yellow needles and prisms. It was, however, thought desirable to systematically study the conditions under which the nitrites are formed.With this acid (1 : 4), the needles begin to appearin the course of about half an hour, and at the end of 24 hours a considerable crop is obtained. As, however, the crop thus formed on the surface of the mercury acts as a protective layer, thereby hindering the action of the liquid on the metal, the salt ceases to grow; the deposit of the nitrite, thereFore, should be removed, and the mercury and liquid carefully decanted off into another beaker, when a second crop will be obtained the next day. By repeating the process, successive crops can be col- lected from day to day. B. Nitric acid (1 : 6).-The first crop of crystals of mercurous nitrite was collected next day, and two others at intervals of 5 days, but a * I avail myself of this opportunity to express my sincere thanks to Mr.N, Chandra Nag, M. A., Junior Assistant, Chemical Department, for his assiduous and ungrudging help in making the nitrogen estimations.CONDITIONS UNDER WHICH THEY ARE FORMED. 339 small quantity of the crystals of nitrite from the last crop was left with the mother liquor and the excess of mercury ; 1 2 days afterwards a single, colourless, bright crystal was observed, and 2 days after this a large crop of the same kind of crystals was collected. This salt, on analysis, was found to be that described below as ‘ I Marignac’s salt.” C. Nit~ic acid (1 : l).-The action was immediate and very energetic, torrents of red fumes being evolved, and the liquid turning bluish to greenish ; after about half an hour, the action seemed almost to cease.At the end of about 20 hours, a crust of long, colourless needles was formed ; the lower part of the crust, however, consisted of the yellow nitrite mixed with the former. D. Nitric acid (1 : 2).-The action was somewhat less energetic, the product consisting practically of yellow salt, a small portion only being transformed into colourless needles. Beliaviour of &t&c Acid towcwds Mewus*ous Nitvite. Strong nitric acid, in the cold, has no immediate action on the salt ; but, after a few minutes, energetic action sets in. I f themixture is heated immediately after adding the strong nitric acid, a violent action begins, copious red fumes are given off, and a clear solution of mercuric salt is obtained.If, after adding strong nitric acid, a small quantity of water is poured in, action a t once commences, nitrous fumes are evolved, and the liquid becomes bluish; a t the same time, a few glo- bules of mercury separate, but disappear on warming the liquid, which contains both mercurous and mercuric salts. If, however, the salt be treated with cold, dilute nitric acid, the action is very slow, bubbles of gas being given off a t intervals ; it is only after the action has con- tinued 3 to 4 days that the salt dissolves, and colourless crystals of mercurous nitrate (“ Marignac’s salt ’7) crystallise out. In$uence of the psesence of Nitvow Acid irz promoting the fwmation of the Nitrite. Russell,* Divers,? and, lately, Veley $ have come to the conclusion that it is the nitrous acid present in the nitric acid that plays the prominent part in the dissolution of metals like silver, mercury, and copper, &c.In order to decide what advantage, if any, would be gained if nitrous acid were initially present, three parallel experiments mere started si m ul t aneousl p. 1.-50 C.C. of colourless nitric acid, sp. gr. 1.410, diluted mith 150 C.C. of water, to which mas added an excess of mercury. * C. S. J., 1874, 27, 3. -t. Ibid., Trans., 1883, 43, 443 ; Trans., 1885, 47, 231. Proc. IZoy. Soc., 1890, 48, p. 458.340 RAY: THE NITRITES OF MERCURY AND THE VARYING 11.-The same as above, with n few drops of red fuming nitric acid. 111.-The same as in I, with 5 C.C. of red fuming nitric acid. In I, after the lapse of about 15 minutes, there was scarcely any depo- sit of yellow needles, in I1 the deposit was distinctly visible, in I11 more so; after the lapse of another hour, a deposit was formed in I; in fact, the amounts in I and I1 were much the same ; whilst in I11 i t was some- what larger. Next day, the yield was found to be practically the same in all three.It is evident, therefore, that nitrous acid over and above that present even in colourless nitric acid, gives a slight advantage at first, but this disappears in the long run. I . Monhydmted Mercurous Nitrite. 11. Bask Mwcuroso-mercuyic ATit&es ; ic?zd 111. Mercuric Nitrite. Mercurous nitrite, Hg,(NO,),, has been shown to undergo partial de- composition when treated with water, thus: Hg,(NO,), = Hg(NO,), + Hg.Nearly 22 per cent. of the salt, however, remains in solution CGS suck. When the solution was hot and concentrated, it was noticed that a yellow, powdery mass separated on cooling, and, on analysis, this was found to be the unaltered nitrite, Hg,(NO,),. On allowing a some- what dilute solution to evaporate spontaneously in a shallow dish, tho salts mentioned above were obtained in succession. A detailed descrip- tion of each is given below. I. Monhydrated Mercurous Nit?-ite : Hg,(NO,), + H,O.-In the course of 2 to 3 days a crop was obtained consisting of glistening, pale, lemon- yellow prisms. The action of water on this salt is precisely similar to that on mercurous nitrite. When kept in contact with water for some time, metallic mercury, in a fine state of division, begins to separate.The method of analysis was the same as that employed for mercurous nitrite. For results, see Table. On comparing the result with that of mercurous nitrite, it would ap- pear that the rate of dissociation of this hydrated salt is differer,t, although in its general behaviour it resembles the former. (Vide B I, 11, 111, Table, p. 345.) That the present salt contains water of crystallisation is proved by the fact that, when kept in the desiccator over strong sulphuric acid, it effloresces somewhat ; but the former salt, Hg2(N0,),, neither loses in weight nor in brilliancy under similar conditions. As the analyses given represent different preparations, it is evident that a salt of constant composition is always formed. Of the several salts described in the present paper, this is the only one which yielded crystals big enough for measurement.Mr. T. H. Holland, of the Geological Survey of India, kindly undertook to exa- mine the crystals (see the next paper).CONDITIONS UNDER WHICH THEY ARE FORMED. 341 11. Bccsic n~ercul.oso-s,iercu~~c iVit&es.- Of these there are two, namely, the a-salt, having the formula 9Hg,0,4Hg0,5N,03,8H,0, and the P-salt, €Ig,0,2Hg0,N,0,,2H20. When the triclinic prisms of the above monhydrated salt had ceased to grow, small, orange- coloured nodules began to appear along with them, and then deep yellow clusters of needles or feathery tufts starting from a nucleus. These two basic salts have been named a and respectively. The analyses (see Table, p. 345) belong to two distinct preparations.The behaviour of the present class of salts was entirely different from that of the previous normal nitrites, When kept in contact with water, scarcely any change was noticed, and no separation of mercnry took place, but on agitating with a few drops of dilute nitric acid, they dissolved completely. Dilute nitric acid, therefore, can be used in the diagnosis of the two classes of salts-normal and basic. If diluto nitric acid is poured on the normal salt and the mixture warmed, copious red fumes are at once evolved and an energetic action begins ; a small portion of mercury separates, dissolving slowly in the acid, with gentle effervescence. Nitric acid, in fact, seems to act in a two-fold manner. First, it displaces the nitrous acid, and then dissolves the mercury set free.Mercurous nitrate, for the most part, with only a small proportion of mercuric nitrate, remain in solution. When the salts are 6asic, nitric acid seems first to enter into combina- tion with the base, and if the acid be very cautiously added drop by drop, not the least trace of nitrous fumes is evolved. Dilute nitric acid does not appear t o exercise any oxidising action on these salts. In analysing these salts, they were dissolved, as explained above, and the mercurous and mercuric mercury estimated as calomel and sulphide respectively. (Vide C I-IV, D 1-111, and E I-IX, Table, p. 345). The water in this and the following salts is easily given off when they are gently heated in a test-tube, but it is not given off in the desiccator, even when they are finely powdered ; it seems preferable, therefore, to regard it as ‘‘ water of constitution ” (vide Marignac’s salt,” below).On referring to the table of results of analyses, it mould appear that the mercurous mercury is sometimes too high by 0.6 to 0.8 per cent., whilst the mercuric mercury is too low on an average by about the same amount. The explanation appears to be that none of these salts could be washed or crystallised, and that, during the process of drying on a porous tile, some portion of the thick mother liquor was absorbed by the salts. 111. Mercwic fiiti-ite, 1 2Hg0,5N20,,24H,O.-After the yellow, feathery crystalline tufts of the /3-salt had ceased t o be deposited, the mother liquor was still found to contain distinct traces of the mercnr- ous salt, and the salt which now began to appear consisted of thin342 RAY: THE NITRITES OF MERCURY AND THE VARYING scales, almost white with a faint yellowish tint ; these were, however, slightly contaminated with the mercurous salt. When the mother liquor had evaporated to dryness,very thin scales were formed, adhering t o the bottom of the basin, and consisting purely of the mercuric salt ; these were eztsily detached from the dry, granular residue, com- posed mainly of mercuric nitrite with a slight admixture of the mer- curous salt. These scales, which were almost white with a yellowish tint, were kept over sulphuric acid before being analysed.The presence of water was proved qualitatively. Trccnsformcction of the Nityite into Nitrate.(a) Monl,yd~i6ted Memuyous Nitmte, Hg,(N0J2 + 2H,O.-The cir- cumstances under which the nitrite is transformed into the nitrate have already been alluded to (see ante, p. 341). At first, I came to the conclusion that the nitrate formed is invariably “ Marignac’s salt,” a description of which will be found below. It has lately been observed, however, that this is not the case. When the nitrite is prepared from an acid diluted in the proportion of 1 : 3, the conversion of this salt into a nitrate takes place more rapidly than when dilute acid 1 : 4 or 1 : 6 has been used. Sometimes in the course of two days, or even one day, colourless, soft crystals make their appearance side by side with the nitrite, but they soon disappear to reappear again in another form; they are highly efflorescent, falling t o powder when exposed t o dry air.I n fact, whenever the transformation of the nitrite into nitrate takes place slowly, the more stable “Marignac’s salt ” is formed, and this explains why this nitrate has been so long overlooked by workers in this field. The new mercurous nitrate is sometimes deposited in isolated crystals, and sometimes as a thick crust ; in the latter case, some of the mother liquor always remains enclosed. Pvep. I.-For analysis, small individual crystals were picked out. 1.0388 of the salt lost, in the desiccator, 0.0660 ; loss = 6.35 per cent. 0.1300 of thisdehydrated salt gave 6.2 C.C. moist nitrogen a t 31“ and Prep. II.-0*4406, keptover H2S0,, lost 0.0275 (loss = 6.24 per cent.), 759 mm. and gave 0.3665 of HgS.Theory for Theory for Found. ......... 76.49 H g 71-43 76.33 - N ........... - 5.34 - 5.13 ........ 6.30 (mean) - H,O 6-43 - ,. HgNO3-I- H&. HgNO,. is hydr. salt. 8s dehydr. s k . (a) Narigmac’s salts 5Hg20,3N,0, + 2H,O or 3Hg2(N0,)2 + 2Hg,(OH), or Hg2(N0,)2,4Hg2(OH)N03.-This is the form into which the normalCONDETlONS UNDER WHICH THEY ARE FORMED. 343 nitrite, described above, is ultimately converted. Regarding this compound, the information in Watts’ Diet ioncc~y of Chemisty, edited by Morley and Muir (vol. iii., p. 514) and in Roscoe and Schor- lemmer’s well-known treatise, is very vague and meagre. The BC- count given of it in Fremy’s Encycl. (tome iii., 14“ Cahier, p. 243), based on Marignac’s original memoirs,” is more complete, but the me- thod of preparation, or rather formation, of this salt is different from that described below ; and this probably explains the want of uniformity in the formulaj proposed by Gerhardt and by Marignac respectively. The formation of the nitrite and its ultimate conversion into the nitrate is fully explained in my first paper (Zoc.cit.). In confirmation of the views there put forward, the following proof may be adduced, The residues from several preparations of the nitrite, consisting of mercury mixed up with some nitrite, together with the mother liquor, were in one case stored up in a tall, well-stoppered bottle, but the vessel did not burst, nor was the stopper thrown out. The fact is, there was no pressure of gas inside; the bubbles of nitric oxide during their ascent through the long column of liquid were completely absorbed.At first, mercurous nitrite gradually formed and accumu- lated, but afterwards slowly dissolved, and in the course of about two months a hard crust of Marignac’s salt ” was deposited on the surface of the mercury, from which large, well-formed crystals with sharp edges projected. I am able fully to confirm Marignac’s statements as to the general properties of this salt, The crystals are very hard, and colourless; retain their lustre unimpaired when exposed to the air, and do not lose water over sulphuric acid in a vacuum ; they give up water, however, easily enough when gently heated in a test-tube. It is necessary to bear in mind that the mercurous nitrite is not directly changed into this nitrate, but passes through the transitional form of the monhydrated nitrate Hg2(N0,), + 2H20, although this latter stage oftentimes appears to be omitted.A m Zysis. I. 0.4152 gave 03945 HgS. Hg=81.88. 111. Ob1877 ,, 6.2 C.C. moist nitrogen at 34” and 755 mm. N = 3.47. Theory requires Hg = 81.96, N = 3.44 per cent. This salt is a definite and stable compound, the analytical results fully confirming Marignac’s formula ; nearly a dozen analyses of different preparations were made. This affords independent testimony from a high authority as to the trustworthiness of the methods of * Ann. Chiwz. Phys., 1849, [3], 27, 515. II. 0’3458 ,, 0.3290 HgS. Hg=82.01.344 RAY: THE NITRITES OF MERCURY, ETC. estimating mercury and nitrogen employed throughout the present investigation.I n a future communication, I hope to throw further light on the formation as well as on the constitution of the nitrites described above. flunammq. From the foregoing investigation, it seems to be established- 1.-That by the action of dilute nitric acid in the cold,* the strength varying from 10 to 23 per cent. or so, mercurous nitrite is cclwccys formed. 2.--That the mercurous nitrite thus formed slowly dissolves in the mother liquor, resulting in the production of mercurous nitrate of two kinds (a), monhydrated mercurous nitrate, Hg,(NO,), + 8H20, and (b), the basic nitrate, termed ‘ I Marignac’s salt.” 3.-That when a neutral dilute solution of mercurous and mercuric nitrites (the products of dissociation) is allowed to evaporate spontsne- ously, monhydrated mercurous nitrite, Hg,(NO,), + H,O, two mercuroso- mercuric nitrites, and a basic memukc nitrite are successively formed.4.-That of these salts only two may be said to contain real ‘‘ water of crystallisation,” namely, those termed monhydrated mercurous nitrite and nitrate respectively, in that they are efflorescent, losing water rapidly in a dry atmosphere ; the rest may be held to contain ‘‘ water of constitution.” CHEMICAL LABORATORY, PEESIDENCY COLLEGE, CALCUTTA, July, 1896. * Some commentary is, perhaps, needed on the expression “in the cold,” used throughout. The average temperature of Calcutta at mid-day may be taken as 32.9” in the summer season, whilst in winter it is nearly 22.2”. These temperatures have been obtained from sixteen years’ observation of the thermograph (dry)-at the local meteorological office.Table of Besults of Analyses.2.485 1586 1'436 0'1,452 05125 1.046 05978 0.8334 0.9331 0.3064 0.669 0 451 0.480 0'500 0'5564 0.2032 0 6330 0'4734 0'4126 0.242 0'331 0'4966 0.5116 0'1288 0*188 - Weight found of Free' Hg. - 3.339 - - )'OSO 3 '1 60 3'6814 0.7685 - - - 0.221 0.203 0.243 0'277 0'310 0'236 - - - - - 0.256 - - HgS. - 0.577 1-36 - 0.194 0.392 0'148 0.1654 I - - 0.210 0.202 0.263 0'3015 0'3975 - - - - - 0.235 0'238 0'1054 Percentage of Free' Hg. 'nus Hg. - 18.18 - - 12'26 14-64 69'35 69'95 - - - 41.62 -10.05) 41 13 43'27 - 41.55 42.33 - - - 42.49 - 31.30 - - 32.62 32'34 15-29 15.28 - - - 40.13 40'26 40'0s 41'04 40'72 I - - - 41.31 40.01 1 Percentage found. '01. of moist nitro- gen 111 c.c. Total 7.9 =32"),(p = 758) mm 7'6 it. 32" and 758 mm. 16-4 it 32" and 760 mm. G.0 I t 32" and 756 mm. 80'94 . (mean) 81-70 78-95 1 (mean) 84.94 . (mean) 81-29 1 (mean) 82.35 - 82-59 83.05 6 '6 I I t 31" and 759 mm. 8.9 it 31" and 758 mm. I 8250 70.54 7 '3 .t315" and751 mm. I - N. 5.69 2.67 2'62 3.14 - 2.91 (mean) I 4'09 - Percentage, theoretical. Totall Hg. - 81-30 78-45 85'77 83'32 70'55 - 4'11 I} Remarks . The "free" Hggenerally comes out too low. (Stse anfe, p. 337.) * Estimated ns total mer- cury. (See p. :W.) The range within which the salt is formed is a wide one ; thus the successive crops D I, 11.111, and E I, 111, IV, VLII, and I X , hare the same composition. The crystallisation was started April 1, and the last crop collected May 6, 1896. t Estimated as total mer- cury. the salt being pre- vioully oxidised by means of HNOa