GENERAL AND PHYSICAL CHEMISTRY. 93 In organic C he mi s t r y. Slow Oxidation of Hydrogen and Carbon. By H. HIRTZ and VICTOR MEYER (Bey., 1896, 29, 2828-2831. Compare this vol., ii, 19)-It is improbable that ozone was formed in the earlier experi- ments (Zoc. cit.), as the gas evolved when dilute sulphuric acid acts on potassium permanganate is quite inert, and ozone appears to be pro- duced only when the concentrated acid is employed. Morse, Hopkins, and Walker have shown (Abstr., 1896, ii, 475) that, under certain conditions, finely divided manganese dioxide effects the reduction of potassium permanganate, oxygen being liberated. These conditions, however, were not those employed in the above94 ABSTRACTS O F CHEMICAL PAPERS. experiments, and again only in the acidified permanganate was any appreciable residue observable.Later experiments have shown that acidified permanganate ' solutions in contact with manganese dioxide yield only 12.5 per cent. of the volume of gas obtained when hydrogen is present, The difference in volume between the amount of oxygen obtained when the permanganate solution is quiescent, and when it is strongly agitated, has suggested the idea that the action is a reversible one; experiments made with the object of observing any absorption of oxygen under the conditions employed have given negative results, thus rendering the suggestion improbable. A. L. Purification of Water by Distillation. By GEORGE A. HULETT (Zeits. physikal. Chem., 1896, 21, 297--301).-The author recommends the use of a condenser conOaining an inner tube of platinum, narrowed slightly a t the lower end, and with the upper end projecting about 15 cm.into the neck of the retort employed for the distillation. The space between the platinum tube and the neck of the retort is packed with asbestos, and by this means only the water actually condensed in the platinum tube is collected. Ordinary distilled water which had been allowed to remain over potassium permanganate or potassium dichromate and sulphuric acid, when distilled over barium hydroxide in this apparatus, gave a distillate of speedily diminishing conductivity, the value 0.76 x 10-lO being reached before one-fourth of the water had distilled. 30 barium hydroxide appears to be carried over, but, if it is not employed, sulphuric acid may occur in the distillate.L. M. J. Nitrites in the Air. By GEORGE DEFREN (Chem. News, 1896, '74, 330-231).-Re-distilled water, free from ammonia, nitrites, and nitrates, was exposed t o the air in well-ventilated rooms, in porcelain evaporating dishes 15 cm. in diameter; each dish contained 100 C.C. of the water, the superficial area exposed being 95 sq.cm. The water was ex- amined at intervals for nitrites, the quantity being computed by com- parison with a standard solution of potassium nitrite containing, per c.c., 0*0000001 gram of nitrogen as nitrite, the conditions as regards burning gas jets and lamps being noted. Under varying conditions, the quantity of nitrite, in terms of C.C. of standard, found, after one hour, was 2.5, 3.5 and 8 ; after two hours, 3*5,8*5 and 13.5 ; after seven- teen hours, in the last instance, 84.2 ; and after nineteen hours, in the first and second instance, respectively 57.2 and 72.7.The results show that, where gas is burning, nitrites exist in the air even in well-ven- tilated rooms, and that water absorbs these nitrites in quantities in- creasing with the time of exposure t o the polluted air: D. A. L. Tetrametaphosphimic Acid. By HENRY N. STOKES (Amev. Clzenz. J., 1896, 18, 780-789. Compare this vol. ii, 28.)-Y'etrameta- phospl&nic acid, P4N408H8 + 2H,O, is best prepared by the action of water on tetraphosphonitrilic chloride, P,N,Cl,, dissolved in ether free from alcohol. Chlorhydrins are formed as intermediate products, but remain dissolved in the ether, the acid crystallising in needles fromINORGANIC CHEMISTRY.95 the aqueous portion. The oily chlorhydrins, when separated, and warmed with dilute hydrochloric acid, yield the acid, cry s t a k i n g in colourless needles. One hundred parts of water at 20” dissolve 0.64 part of the crystallised acid; it is somewhat more soluble in boiling water, but insoluble in alcohol. Boiling alkaline solutions cause no evolution of ammonia, and heating with moderately strong hydrochloric or nitric acids brings about but little decomposition. The water of crystallisa- tion is not given off in a vacuum over sulphuric acid, but when heated at 100” the crystallised acid loses weight rapidly, although the theoretical loss is never reached owing to intramolecular changes, in which a portion of the water takes part.It forms three series of saltts, P4N408H6M’2, P4N408H4M’,, and P4N40sM’s. Dip0 t ussium tetvccme taphosplkw~ te, P,N,O,H,K 2, was prepared by adding excess of acetic acid to a solution of the acid in cold, dilute caustic potash. On warming, the salt is deposited as a heavy, sandy powder, consisting of microscopic, thick, rectangular (? quadratic) prisms with basal planes; it is very sparingly soluble, even in boiling water. The tetrapotassium salt, which is very soluble, forms large, flat, obliquely-terminated plates. The tetrccsodiunz salt, P,N,O,H,Na, + 24 (1) H,O, forms obliquely-terminated, flat prisms ; it is sparingly soluble in cold, but readily in hot water. The teti*ammonium salt, P,N,O,H,(NH,), + 4H20, is obtained by treating the acid with strong ammonia, and usually forms well-de- veloped, flat, monoclinic prisms ; it dissolves readily in water, but with difficulty in strong ammonia.The dinmmoszizcm salt, P,N,O,H,( NH,),, is precipitated from a solution of the neutral salt on strongly acidify- ing with acetic acid and warming ; it forms four- and six-sided prisms (1 tetragonal), and is very sparingly soluble, even in boiling water. The burium salt, P,N,O,H,Ba, + 2H20, forms microscopic needles. No definite results were obtained in the attempt t o prepare a mag- nesium salt. The manganese salt forms characteristic, pink, rectangular plates. Ferric chloride when added to a dilute soliition of the neutral ammonium salt gives, on warming, a white, amorphous precipi- tate soluble in much warm hydrochloric acid.The tetnx-siZz;eq* salt, Y,N,O,H,Ag,, is obtained on adding a solution of silver nitrate to one of the free acid. When the precipitation takes place in the cold, the salt is granular or amorphons, but is crystalline when formed in hot solutions. The octo-silver salt, P4N40sAg8, is obtained as a yellowish, flocculent precipitate when an ammoniacal solution of the acid is added to an excess of silver nitrate ; on the other hand, a solution of a neutral tetrametaphosphimate added t o an ammoniacal silver nitrate solution, produces a white, flocculent precipitate. If a solution of the latter in ammonium nitrate is boiled, an orange-yellow, semi- crystalline precipitate is formed. The white and the yellow mm- pounds give on analysis almost the same number?, and are regarded as tautomeric forms corresponding with the acids [PN(OH),], and (PO*NH*OH),.The author discusses the probable constitution of tetrametsphosphimic acid, and calls attention to the fact that, in its general properties, it differs markedly from the trimetaphosphimic acid previously described by him. A. C. C.96 ABSTRACTS OF’ CHEMICAL PAPERS. Uniformity of the Distribution of Argon in the Atmosphere. By TH. SCHL~SING, JUN. (Con2pt. remcl., 1896, 123, 696-697. Compare Abstr., 1896, ii, 166 and 219).-The author has made determinations of argon in samples of air collected in places widely separated, and taken at various distances (a few metres to 2,275 m.) from the earth’s surface. His numbers, which are very concordant, show that argon is uniformly distributed in the atmosphere, and that every 100 volumes of the mixed nitrogen and argon contain 1-192 volumes of the latter gas. This is in strict accordance with his previously published number.A. C. C. A Method of Preparing Double Silicates of Potassium and other Metlals. By ANDRB DUBOIN (Compt. ?*end., 1896, 123, 698- 700).-By dissolving a mixture of magnesia and silica in fused potas- sium fluoride and then submitting the product to prolonged fusion with potassium chloride, the author has obtained both a double silicate of magnesium and potassium, and two compounds containing fluorine in addition, 4KF,SiO, + 3Mg0,2K20, 1OSi0, and ZMgF,,SiO, + 4( K,O,MgO,SSiO,) (see Abstr., 1895, ii, 351). Beryllium oxide dissolves in fused potas- sium fluoride, and when submitted to the treatment described above, gives a crystalline product which appears to be homogeneous, but really consists of a mixture of isomorphous compounds.These are not analo- gous in composition t o the double silicates of magnesium and potassium, but vary between 2K20,3Be0,7Si0, and 2K20,3Be0,5Si0, ; moreover, no double silicates containing ffuorine could be prepared as in the case of magnesium. On adding baryta to fused potassium fluoride contain- ing dissolved silica, a crystalline double silicate having the formula K20,2Ba0,3Si0, (sp. gr. = 3-78) was obtained. If this mixture is fused with potassium chloride, three compounds are formed, the principal one having the formuIa K20,7Ba0,8 SiO,, but containing a little fluorine. Double silicates could not be prepared in the case of calcium, the products always containing chlorine or iInorine ; mixtures of crys- talline products were obtained, only one of which, having the formula 4KF + K20,5Ca0,6Si0, could be isolated.Rubidium Dioxide. By HUGO E m u ” and PAUL KOTHNER (Amwden, 1896, 294, 55-7 l).-The authors have investigated the inflammable nature of metallic rubidium, in order to ascertain whether the spontaneous combustion of this substance on exposure to air, observed by Bunsen in 1863, is due to the influence of oxygen or of moisture, The methods hitherto adopted for the production of metallic rubidium are very unsatisfactory, and the authors describe a convenient and safe process by which 85 per cent. of the theoretical quantity of the metal may be obtained from rubidium hydroxide.A seamless iron tube, of 15 mm. bore, 1 metre in length, having walls 3 mm. thick, is bent a t an angle of 125” about 15 cm. from one end, fitted at the elbow with a loose plug of clean, long, steel shavings, and heated to redness while a current of hydrogen is passed through it ; 30 grams of A. C. C.INORGANIC CHENISTRY. 97 freshly fused, anhydrous rubidium hydroxide is rapidly crushed to a coarse powder with magnesium filings (10 grams), in a warm mortar, and transferred to the long arm of the tube. This is placed in a small combustion furnace, with the short arm dipping beneath the surface of paraffin oil in a porcelain vessel, a gentle current of hydrogen, free from arsenic and dried by means of sulphuric acid and phosphoric anhydride, being passed through the tube; the temperature is cautiously raised, the application of heat being interrupted as soon as the increase in the current of gas indicates that the action has begun.When hydrogen is no longer evolved from the rubidium hydroxide, the temperature of the tube is raised to a red heat, and after half an hour the metal distils over, 14 grams being obtained from the quantity of hydroxide mentioned. When obtained in this manner from rubidium hydroxide prepared from ferric rubidium alum (Erdmann, Abstr., 1894, ii, 351), the metal is in a highly purified condition, and forms a convenient source of salts required for physical investigations ; it melts at 38.5', and has a sp. gr, = 1.5220 at 15'. Rubidizcna dioxide, RbO,, is obtained by the action of dried oxygen on the metal at common temperatures.I n view of the fact that burning rubidium attacks glass, porcelain, platinum, silver, and rubidium chloride, it is necessary to allow the metal to fall into an aluminium dish which lies in a small glass flask filled with nitrogen ; the whole apparatus is then weighed, and when the metal is converted into oxide, it is again filled with nitrogen, and weighed. The metal quickly melts when a stream of oxygen plays on it, and becomes ignited if the current of gas is not checked; when the oxidation proceeds in a normal manner, however, the metal preserves for some time the appearance of molten gold, but finally swells and becomes black, and then ceases t o absorb the gas. On raising the temperature to 500°, it again begins to absorb oxygen, probably owing to the presence of metallic particles previously protected by oxide from the action of the gas, the volume becomes reduced, and a viscous, black liquid is produced ; after this stage has been reached, no more oxygen is absorbed, and on cooling the apparatus, the oxide crystallises in dark brown plates.The authors have obtained no evidence of the existence of other oxides of rubidium, and the dioxide they describe may be heated at a high temperature without losing or absorbing oxygen ; it acts violently on water, however, yielding rubidium hydroxide and hydrogen peroxide, oxygen being liberated. When rubidium dioxide is gently heated in an atmosphere of hydrogen, rubidium hydroxide, water, and oxygen are produced, a result which the authors attribute to the intermediate formation of hydrogen peroxide, in accordance with the equation 2Rb0, + 2H, = 2RbOH + H,O, ; if the action proceeds at too high: a temperature, violet light is developed, less water is formed, and the aluminium dish is corroded, rubidium aluminate, RbAlO,, being produced.It is convenient to employ an aluminium dish for the preparation of rubidium dioxide, because this metal is not wetted by molten rubidium, and it also resists the action of the fused dioxide at temperatures below 500O. M. 0. F,98 ABSTRACTS OF CHEMICAL PAPERS. Double Salts of Rubidium. By HUGO ERDMANN and PAUL KOTHNER (Annalen, 1896, 294, 71-79. Compare Abstr., 1894, ii, 35 I).-Ferric rubidium, ferric ammonium, and ferric potassium alums melt respectively at 53", 43-44', and 33", and comparison of rubidium double salts with the analogous ammonium salts reveals the fact that ammonium more closely resembles rubidium than it does potassium.Rubidium magnesium phosphate, RbMgPO, + 6H,O, separates imme- diately on adding a warm solution of magnesium chloride to a mixture of rubidium chloride and disodicm phosphate dissolved in water, the amorphous precipitate rapidly becoming crystalline ; it is decomposed by silver nitrate, but resists the action of boiling water. Hydrogen rubidium magnesium carbonate, HRb3Xg(C03), + 4H,O, is obtained by saturating an aqueous solution of rubidium carbonate with carbonic anhydride, and heating the liquid with magnesium carbonate during 5 minutes a t 60°, a current of carbonic anhydride being passed through the liquid meanwhile; the filtered liquid deposits minute, transparent rhombs, having the edges flattened.The salt effloresces in a few days when exposed to air, and in this respect resembles hydrogen ammonium magnesium carbonate, whilst the potassium salt may be preserved for years without undergoing change. Lead m,bidiurn chloride, P bRb,Cl,, is obtained under the conditions observed by Friedrich, in .preparing the analogous ammonium salt (Abstr., 1893, ii, 415); it is a yellow, crystalline powder, which closely resembles lead ammonium chloride. Concentrated sulphuric acid acts on it, liberating hydrogen chloride, and precipitating lead tetrachloride as an oil (compare Zoc. cit.), whilst the dilute acid con- verts the metals into sulphates, and liberates chlorine. Rubidium chloride may be precipitated almost quantitatively from its solution in methylic alcohol saturated with chlorine by adding a solution of lead tetrachloride, the precipitate being washed with 80 per cent.alcohol. Lead potassium chloride is much less stable than the rubidium salt, and evolves chlorine when dried in the air ; the same change takes place when the rubidium salt is heated, the tetrachloride, PbRb,CI,, being produced. The rubidium salt is also indifferent towards dilute hydrochloric acid and 96 per cent. alcohol, the potassium salt being decomposed by both agents ; the changes produced under the influence of water and ammonia are less rapid than those which the potassium salt undergoes.I n spite of these differences in behaviour, the estima- tion of rubidium in presence of potassium by means of lead tetra- chloride is inaccurate ; this agent, however, may be employed for the production of purified rubidium chloride from a solution containing 2 per cent. of potassium chloride. Rubidium salts also resemble ammonium salts in respect to their volatility, and it is not possible to remove ammonium chloride from rubidium chloride by application of heat, without loss of the rubidium salt. Traube has shown that the atomic solution volume of rubidium is equal to that of ammonium (Abstr., 1895, ii, 70). By OTTOEAR ~ U L C (Zed. anorg. Chm., 1896, 12, 18@-181).-The author points out that the product M. 0. F. Electrolytic Silver Peroxide.INORGANIC CHEMISTRY.99 of the electrolysis of silver nitrate which he recently described (Abstr., 1896, ii, 521), and to which the formula Ag,NO,, was ascribed, may be regarded as a compound of silver peroxide and the heptoxide of nitrogen, and as being of the composition 7Ag202,N,07. The proper- ties of the compound are consistent with this formula. H. U. Peroxides in their Relationship to the Periodic System of the Elements. By AUGUSTO PICCINI (Zeit. arnorg. Chem., 1896, 12, 169-1 79).-The author considers peroxides of the hydrogen peroxide type, such as BaO,, TiO,, and S20,, in their relationship to the periodic system and to the question of the type of the highest oxygen compounds. As a general characteristic of oxides of this class may be quoted their reduction in acid solution by such oxidising agents as MnO,, PbO,, and KMnO,.This distinguishes the peroxides from all other classes of oxides, and the peroxides are also distinguished by their lack of the acidic character that usually attaches to the higher oxides. These and other marked differences between the peroxides and the ordinary oxides of the water type lead to the conclusion that the peroxides cannot be regarded as compounds typical of the highest combining powers of the elements. H. C. Double Bromides. By RAOUL VARET (Con@. vend., 1896, 123, 497--500).-The author has measured the heat developed on mixing aqueous solutions of mercuric bromide and of other metallic bromides capable of forming double salts of the type BHgBr2,RIBr2,nH?0, or HgBr2,MBr2,nH,0, experiments being made with solutions of difierent degrees of concentration.As a rule, the development of heat is greater the more concentrated the solutions, and it is also increased by the presence of an excess of the soluble bromide. Similar experiments were made with cobalt and manganese bromides, and sodium and ammonium bromides. The heats of formation in sohtion of the compounds of mercuric bromide with other metallic bromides are of the same order of magni- tude for a given series of double salts, any differences that are observed being due t o the unequal thermal effects resulting from dilution in different cases. The results lead to the conclusion that these double salts are derived from complex acids, such as H,Hg,Br,: and H2HgBr,. The double salts formed by cobalt or manganese bromide with sodium or ammonium bromide are dissociated to a large extent on dialysis, and the thermal effects produced by mixing diluta solutions of their proximate constituents are very slight;.By VICTOB BIERNACKI (Ann. Phys. Chem., 1896, [ Z ] , 59,664-667).--8 rod or wire of aluminium can be readily amalgamated by connecting it with one pole of a bat'tery the other pole of which is connected with mercury, and then dipping the nlu- minium into the mercury and removing it again several times. The sparks formed each time at the connecting surfaces serve to heat the aluminium sufficiently t o induce combination with the mercury. As the mercury in the amalgam appears t o play the part of a catalytic agent, the smallest quantity of mercury at the end of an aluminium C.H. B. Aluminium Amalgam.100 ABSTRACTS OF CHEMICAL PAPERS. wire will bring about oxidation of very considerable amounts of aluminium. H. C. The Constitution of Inorganic Compounds. By ALFRED WERNER and ARTURO MIOLATI (Zed. physikal. Chem., 1896, 21, 225-- 238).-The authors determined the electrical conductivity of various ammoniacal cobalt compounds with a view to the elucidation of their constitution. The conductivity of Jorgen sen’s dini trotriaminecobal t chloride (Abstr., 1895, ii, 48) increased with the time, reaching a final constant value consistent with the presence of a univalent cation. The chlorine is, therefore, not present originally in the ion state, and hence cannot be united to the amine group, as Jorgensen supposed. The trinitrotriamine compound, Co(NH,),(NO,),, also contains no ion, the value for the conductivity being very low-1.6 a t U = 1000, ant1 totally different from that of the croceocobaltic nitrite, NO,*Co(NO,),(NH,), ; ,A = 90 at = 1024.The nitritochlorotetraminecobalt chloride, Cl*Co{NO,Cl(NH,),), originally gave the value p = 68 (U = 240), but after remaining for 70 minutes at Oo, the value had increased to 104, this being due probably to hydrolysis into Co(NO,H,O(NH,),}Cl,. The praseo-salts appear to undergo an analogous hydrolysis, from Co( (NH3),C12}Br into CO((NH,),(H~O)~)C~,B~, as the conductivity increased in 40 minutes, from 116.6 to 332.1 with a final maximum = 372 ( u = 512), the nitrite and nitrate exhibiting similar changes. The hydrogen sulphate, how- ever, only gave an increase of from 373 to 439 (V = 256) so that, in this case, the final compound appears to be Co{(NH,),H,OC1)SO4, the con- ductivity of which in 1/256 HCl solution is 439.7.The diaquodichloro- diamine salts, Co{ (NH3)2(~O),Cl,)Cl, also gave a marked increase after ft time,corresponding with the ionisation of the two chlorine atoms. The sulphato-pentamine compounds contain the complex ion, whilst a rapid increase of conductivity by dilution indicated hydrolysis to Co(NH,),H,O. The chloropentamine, aquopentamine, and aquo- chlorotetrnmine salts were also examined, and, as in the previous cases, the results indicated hydrolysis to aquo-salts, and were in complete accord with the author’s views of the constitution of these compounds. (Abstr., 1894, ii, 407.) L.M. J. Nickel Dioxide and its Acid Properties : Barium Nickelite. By EM. DUFAU (Compt. Tend., 1896. 123, 495-497).--When an inti- matemixture of nickelic oxide (85 parts) with barium oxide (155 parts) or barium carbonate (200 parts) is surrounded by barium oxide and heated for 10 minutes in the electric furnace with an arc from 60 volts and 300 amphres, a fused, grey mass is obtained with a crystalline frac- ture, It soon disintegrates when exposed to the air, and when rapidly treated with cold water, levigated, and finally washed and levigated with alcohol, it yields small, brilliant, dark-coloured crystals, whichINORGANIC CHEMISTRY. 101 are greenish-brown when powdered ; sp. gr. = 4.8 at 20" ; hardness a little above 4. The crystals consist of barium dinickelite, BaO,2NiO,, and are somewhat unstable.Cold water attacks them slowly and hot water rapidly. Hydrofluoric acid dissolves them with effervescence, and hydrochloric acid, with evolution of chlorine ; nitric acid and ammonia, also dissolve and decompose them. Chlorine, bromine, and iodine attack the nickelite at a red heat, with formation of halogen salts of the metals, but oxygen has no action a t bright redness. Sulphur, a Iitt'le above its melting point, converts the nickelite into sulphides, with incandes- cence. Hydrogen fluoride and hydrogen chloride decompose it at ared heat, but fused neutral oxidising agents are without action on it. It follows from these observations that nickel dioxide not only exists but has acid properties analogous to those of cobalt and manganese dioxides.Since nickelic oxide has no acid properties, it is probable that the oxide Ni,O, has the constitution Ni0,,2NiO. U. H. B. Diffusion of Sulphides through Steel. By EDWARD D. CAMP- BELL (Amel.. Chern. J., lS96, 18, 707-719).-Ferrous sulphide, cuprous sulphide, rickel sulphide (Ni,S3}, and the product obtained by melting together ferrous sulphide and iron ( 8 subsulphide of iron) are incapable of diffusing through steel bars heated t o bright redness. When a mixture of 400 grams of ferrous sulphide with 13 per cent. of its weight of mag- netic oxide of iron was melted, a product was obtained which the author regards as impure oxysulphide of iron, Fe,OS; this was found to diffuse readily through red-hot steel bars and to have the property when mixed with cuprous sulphide, of carrying this with it.It is suggested that Fe,OS, being at the temperature of the experiments an extremely mobile liquid (as shown by its rapid passage through the walls of the clay crucible used in its preparation}, is able to diffuse through the steel on account of the porosity of the latter substance a t a bright red heat. A. C . C. Influence of Heat Treatment and of Carbon on the Solubility of Phosphorus in Steels. By EDWARD D. CAMPBELL and 8. cy/. BABCOCK (Ame?*. Cheni. J., 1896, 18, 719--723).-The authors have in- vestigated theinfluence of the percentage of carbon in steel, and of the slow or sudden cooling of the latter on the solubility of the contained phosphorus. Estimations were made of the percentages of phosphorus (cc) soluble in a neutml solution of mercuric chloride, ( h ) insoluble in mercuric chloride but soluble in 4 per cent. hydrochloric acid, and ( c ) insoluble in either of the above two liquids, and the following conclu- sions are arrived at :-(1) With very low carbon percentsges, the rate of cooling of the metal has but little effect on the solubility of the phosphorus ; (2) with increase of carbon, hardeniag diminishes the solubility, and (3) with high carbon percentages the solubility of the phosphorus .is increased by slow cooling. It is suggested that these Yesults point to the probable formation at a high temperature of a difficultly soluble compound of iron with carbon and phosphorus, which passes on slow cooling into an easily soluble one. A. C. C. VOL. LXXII. ii. 8102 ABSTRACTS OF CHEMICAL PAPERS, Bismuth Oxyiodide. By T. R. BLYTH (Chem. News, 1896, 74, 200).-The residue from the distillation of the double iodide of methyl- arnine and bismuth with caustic soda, and the product of boiling bis- muth oxyiodide, BiOI, with the same reagent, both have a compo- sition correspouding with the formula Bi,71,0,, = Bi13,8Bi,0, = 3BiOI,'TBi,03. It is a light, microscopically crystalline powder, with a very slight brown tint, soluble in dilute hydrochloric acid, not attacked by boiling water or alkalis, but is decomposed by nitric acid with liberation of iodine and by hydrogen sulphide with formation of sulphide. D. A. L.