On some Combinallons of Plathmm. 337 



a brown co!our,'ancl has some degree of tenacity ; but when well 

 washed and dried at a temperature a little above the boiling 

 point of water, its colour changes to a jet black ; it becomes 

 hard and brittle, and has a resinous lustre. It is not decomposed 

 by being boiled in water or in weak alkaline solutions. When 

 it is gently heated by a spirit-lamp on a slip of platinum, a vio- 

 lent action is produced, and a dense white vapour is exhaled, in 

 which the odour of sulphureous acid is perceptible, the substance 

 becomes ignited, and is presently decomposed, leaving the re- 

 duced platinum in small grains. 



When tliis compound is decomposed by heat in close vessels 

 over water or mercury, it yields a gray sulphuret of platinum*, 

 nitrogen, sulphureous, carburetted hydrogen and carbonic acid 

 gases, carbonate of ammonia, and an oily-like fluid. This com- 

 pound of sulphate of platinum and gelatine, when dried at a heat 

 just above that of boiling water, aflbrded, by its decomposition 

 in two experiments, half its weight of platinum ; and if my for- 

 n)er statement of the com])osition of sulphate of platinum is cor- 

 rect, 100 grains of the above compound will consist of about 



56-11 oxide of platinum, 



20"02 sulphuric acid, 



23-87 gelatine and water. 



100-00 



6. On the Sulphate of Plulhmm, as a Test for Gelalifie. 



As I found that minute quantities of gelatine in solution were 

 readily detected bv the sulphate of platinum, 1 n)ade .some c\- 

 jjcriments to ascertain the efficacy of this substance as a test for 

 gelatine, and I am inclined to think it meiits a deciiled prefe- 

 rence over the reagents at present used by chemists for this pur- 

 pose. The best known substances for detecting the presence of 

 gelatine are, 1 presume, those whicli contain the tanning princi- 

 ple, as the infusions of oak-bark, nutgalh, catechu, &:c. And a 

 varietv of gelatine, isinglass, (as is well known,) is employed to 

 ascertain the quantity of tanning prlncijjle in ditfevcnt astringent 

 substances; but for this jjurpose, as Sir H. Davy has shown f, 

 many precauticms are necessary; and from his experiments it 

 ap|>ears that tamiin may exist in a state of combination, in which 

 its presence cannot be made evident by means of a solution of 

 gelatine. 1 have made several comparative experiments on the 

 efficacy of those astringent infusions, and of the sulphate of pla- 



* In the Annales dc Chimie, &c. tome v., I\I. Vauquclin treats of the snl- 

 phurtt of platinum as a new compound whicli he had formed; but I pub- 

 fislu'd an account r.f it in the PhilosopTKcal Majrazine in the year 1812. 



t rhil. Tranv IHO.'J.— I'hil. Mag. vol. xvi. No. (il. p. 82. ' 



Vi.1. 56. Ko. 271. A't'i'. ISl-iO, I' u tinum, 



