192 Notice of some Recent [March 



state of crystals by passing the vapour of chloro-chromic 

 acid through a red hot glass tube. # A mixture of chlorine 

 and oxygen is formed, and the crystals of oxide are deposited 

 in the tube. Thus prepared, it is not green but black, pos- 

 sessing the metallic lustre, and has the same form as 

 native peroxide of iron, (fer digiste or rhombohedral iron 

 ore) which he considers a proof of the ismorphism of these 

 two oxides. The spec. grav. in the crystallized state differs 

 little from that of peroxide of iron, being 5*21. 



It scratches rock crystal, hyacinth, and cuts glass. In 

 the crystallized state it is therefore as hard as corundum, 

 which, with the exception of the diamond and rhodium, 

 is the hardest of known substances. Chloro-chromic acid 

 was discovered by Professor Thomson in 1824, and is pre- 

 pared by distilling in a glass retort 500 gr. sulphuric acid, 

 with 190 gr. dry bichromate of potash, and 225 gr. of 

 decripitated common salt. According to Dr. Thomson, it 

 consists of one atom chlorine, and one atom chromic acid. 

 Rose considers it a combination of two atoms chromic acid 

 and one perchloride of chromium. Wbhler prepares it by 

 distilling ten parts common salt, 16*9 neutral chromate of 

 potash, and thirty parts of concentrated sulphuric acid. 



SALTS. 



Crenate of potash and crenate of soda form a yellow extract 

 looking mass, which becomes hard and cracks, and is neutral 

 to test-paper ; soluble in absolute alcohol ; scarcely soluble 

 in spirits of the sp. gr. 0*86. When heated gives out fumes 

 smelling of tobacco, and leaves alkaline carbonates. 



Crenate of Ammonia leaves in the air a brown extractive 

 matter which reddens litmus paper. In this state it contains 

 much ammonia, which maybe separated by potash or lime. 



Crenate of barytes is so slowly soluble in water that it 

 may be precipitated in a yellow flocky state, but is dissolved 

 by the addition of more water, and leaves a kind of varnish 

 on the vessel. 



Crenate of lime is more easily soluble, but can be precipi- 

 tated. Its solubility is much affected by the presence of 

 other salts. It precipitates in pale yellow flocks, when a 



* Ann. de Chim. lvii. 105. 



