On some Comhinahons of Platinum. 335 



of its being a true chemical compound. It seems rather doubt- 

 ful, whether the powder can be regarded as a sub-nitrate of 

 platinum, or a combination of platinum with oxygen and nitro- 

 gen, in a different state from that in which they co-exist in the 

 nitrous acid. On the idea that the powder is a compound of 

 the metal with a little oxygen and nitrous acid, something may 

 be said on the mode of its formation, and on the more remark- 

 able properties it exhibits. 



From the manner in which the sulphate of platinum is formed 

 (namely, by the agency of nitrous acid on the hydro-sulphuret 

 of platinum), there can be no difficulty in accounting for the 

 presence of a small portion of nitrous acid in it; and my ex- 

 periments incline me to the opinion, that it is scarcely possible 

 to separate the last portions of nitrous acid from the sulphate, 

 without entirely decomposing it. That the quantity of nitrous 

 acid in the sulphate must, however, be very limited, appears 

 from this circumstance, that the addition of a little nitrous acid 

 to the sulphate, entirely prevents the formation of the black 

 powder, though successive portions of alcohol be added, and the 

 whole boiled for a considerable time. 



When sulphate of platinum, containing a Httle nitrous acid, 

 is treated with alcohol, a mutual action takes place ; slowly at 

 the common temperature of the air; but rapidly by the assist- 

 ance of heat : the sulphuric acid being united to the oxide of 

 platinum by a weak affinity, seems to form a new combination 

 with the alcohol, whilst the oxide combines with the portion of 

 nitrous acid present, to form the black powder. In certain cases, 

 as is well known, alcohol separates salts from their aqueous so- 

 lutions, in consequence of a stronger affinity for the water in 

 Avhich they are dissolved ; but in this instance, the agencies of 

 alcohol and of nitrous acid are probably concerned in separating 

 the sulphuric acid from the sulphate. 



The vivid action of ammoniacal gas on the powder may be 

 referred to the mutual energy with which the alkaline gas, and 

 loosely combined nitrous acid in the powder, act upon each other. 

 1 found by experiment, that ammoniacal gas is absorbed in this 

 instance : thus, three grains of the powder were placed in a gra- 

 duated glass receiver, and filled with dry mercury. 2'3 cubic 

 inches of annnoniacal gas, containing only -j-i- impurity, were 

 let up into the receiver : an immediate action took place, the 

 powder became ignited, and after two hours -Jg- of a cubic inch 

 of the gas were absorbed : recently boiled pure water, whilst yet 

 hot, was let up into the receiver, and the residual gas was all 

 absorbed, except a small globule, which did not exceed the ori- 

 ginal impurity in the ammonia. 



'l"he action of alcohol on the powder is curious, and is ton- 



nected 



