340 On mme Combinaliom of Platinum. 



above results, I am most inclined to place confidence in the lat- 

 ter. There is, indeed, a near coincidence between them, and 

 the difference, w liich is only about one per cent., may be referred 

 to the presence of a little more acid in my first experiments. 

 Tlie gray oxide is insoluble in aqua regia, a fact which seems to 

 add additional support to Sir H. Davy's opinion respecting the 

 action of aqua regia on ))latinum*'. This menstruum, according 

 to Sir H. Davy, does not oxidate platinum, but merelv causes 

 its combination with chlorine. Now, if the metal were oxidated 

 previous to its solution, the oxygen, there is reason to think, 

 would be derived from the nitrous acid, and tbe gray oxide 

 formed by this acid be produced, which can scarcely be the 

 case, as it is insoluble in aqua reeia. Add to this, the fact, that 

 by evaporatiiig a common solution of platinum to dryness, no 

 nitrate can be obtained, but only a muriate, or a compound of 

 the metal and chlorine. 



If, according to the statementsof Professors Vauquelin andBer- 

 zelius, the black oxide of platinum contains about 15 per cent, 

 of oxygen, tiic gray oxide may be considered as tlie protoxide, 

 containing one proportion, and the black oxide one and a half 

 proportion of oxvgen ; and the number representing the element 

 cr proportion in which platinum combines with bodies will be 

 126, taking Sir H. Daw's number 15, to represent the propor- 

 tion in which oxygen unites with bodies. 



Mr. Cooper states the black oxide of platinum to consist of 

 100 platinum, with only 4"31 7 of oxygen f ; but he has, I think, 

 considerably under-rated the oxygen in it. On repeating his 

 experiments on a small scale, I obtained results different from 

 tliose he has stated. Thus, he says the powder obtained from 

 the nuu'iate of platinum by a neutral solution of mercury, is a 

 compound of calomel and the protoxide of platinum ; but by de- 

 composing this powder in a little retort over mercury, I found 

 the neck of the retort partially lined with metallic mercury ; and 

 tills fact alone, I think, is sufficient lo awaken suspicion as to the 

 accuracy of his results. Mr. Cooper, I presume, used a nitrate 

 of mercury to decompose the muriate of platinum, but he seems 

 to have overlooked the nitrous acid in stating his results. 



The chemical historv of platinum is far from being complete. 

 Tbe great want of uniformity in the statements of chemists re- 

 specting the composition of the known compounds of this valu- 

 able metal, and the circumstance of their not harmonizing with 

 the doctrine of definite proportions, prove the necessity of sub- 

 mitting them to a more rigid examination; and this could not 

 be done without rendering our information on the subject more 

 accurate and extensive. 



Coi!t (nstitutioa, Sept. 1, 1319. 



* Joiiniul (jf S: ipnce and the Art.s, vol. i.. f lb. vq\. iii. 



