314- 



the sulphur contained in the salt. The hyposulphite of soda thus 

 obtained gave by analysis a per-centage of hyposulphurous acid, 

 agreeing with 5 as its atomic number, on which supposition it must 

 be regarded as consisting of 2 atoms sulphur, + 1 oxygen ; and this 

 composition he states himself to have verified by direct analysis of 

 several hyposulphites. From this it is easy to derive the composition 

 of the green oxide of chromium, the weight of which thus comes out 

 equal to 5. 



After the description of two compounds, the one of chromic acid 

 and oxide of chromium, and the other of sulphur and the same oxide, 

 obtained by a variation of the circumstances under which sulphu- 

 retted hydrogen is made to act on the chromic salts, the author pro- 

 ceeds to relate experiments in which protosulphate of iron was used 

 as the deoxidizing matter. When a solution of this salt is mixed 

 with one of chromate of potash, a precipitate falls, consisting of green 

 oxide of chromium and peroxide of iron, which, from considerations 

 and experiments detailed at large in the paper, appeared to consist of 

 four atoms peroxide of iron, and one of green oxide of chromium. 



Phosphuret of chromium was formed by subliming phosphorus 

 through red-hot green oxide. It is stated by Dr. Thomson to con- 

 sist of 1^ atom of phosphorus, and 1 atom of the metal. This phos- 

 phuret, by digestion in nitric acid, was converted into phosphate, 

 consisting, according to the author, of 1 atom protoxide, and 1-i- 

 atom phosphoric acid. No sulphuret could be formed by a similar 

 process. The author devotes the next section of his paper to a de- 

 tail of several unsatisfactory experiments for determining the atomic 

 weights of chromic acid and the protoxide, by various processes, in 

 which only partial decompositions were effected. 



He next treats of the brown oxide. It is prepared by passing 

 sulphurous acid through solution of cbromate or bi-chromate of 

 potash. It does not combine with acids ; and when treated with 

 acids, alkalies, or even water, resolves itself into chromic acid and 

 protoxide, of which it appears to be either a mixture or a compound, 

 far from intimate, in the proportion of 1 atom acid to 6 atoms oxide. 



The next section of this paper is devoted to an account of the 

 chloro- chromic acid, a remarkable compound produced by making 

 sulphuric acid act on a mixture of 1 90 parts of bichromate of potash, 

 and 225 parts of common salt. From this mixture, on applying heat, 

 it separates in red fumes, and distils over in a liquid of a rich deep 

 crimson colour, of a sweet astringent acid taste, and strong smell of 

 chlorine. Specific gravity nearly twice that of water, with which it 

 does not mix, but which decomposes it, evolving chlorine and pro- 

 ducing heat. This liquid dropped into oil of turpentine or alcohol, 

 or when poured on sulphur, sets them on fire ; but (what is remark- 

 able) it not only does not fire phosphorus, but even extinguishes it 

 when already inflamed. On other combustibles and metallic bodies 

 it acts with great energy, but without producing ignition. 



In ammoniacal gas, however, it burns vividly. When heated per 

 fc, the chlorine escapee, and a substance resembling green oxide re- 



