for Measuring the Expcvision of Solids. 267 



tlnum, that the mere presence of iron is enough to communi- 

 cate brittleness to that metal." 



Upon inquiry amongst workmen in this country I cannot 

 find that such a property has ever been observed in the course 

 of tlieir experience; and when I consider that the bar in the 

 cavity of the register was perfectly preserved from contact 

 with the iron nails ; and moreover, that it had actually been 

 plunged into melted iron without any change of properties; 

 I cannot suppose that the alteration depended in any way upon 

 this circumstance. 



To resolve these doubts I took 1 1 6 grains of the brittle 

 platinum, which had been ground without difficulty to a fine 

 powder in a steel mortar, and boiled them in nitro-muriatic 

 acid till I had effected a complete solution ; — a little of this 

 solution produced a scarcely perceptible cloudiness in a solu- 

 tion of muriate of baryta. This I have reason to think was 

 owing to a slight impurity in the acids employed; I infer 

 therefore that there was no sulphur in the metal. I proceeded 

 to evaporate the solution; which towards the end of the pro- 

 cess assumed a gelatinous appearance. When in this state, 

 I poured alcohol upon it ; and as the acid still remained in 

 excess, a violent reaction took place with extrication of nitrous 

 gas. I then evaporated to dryness and continued the heat; 

 till the salt of platinum kindled spontaneously, and finally was 

 left in a spongy state. This was again digested in nitro-mu- 

 riatic acid, and the solution carefully evaporated to dryness. 

 The muriate of platinum was then dissolved in water, and a 

 sandy residue remained ; which, when well washed and heated 

 to redness, was of a grayish-white colour, and had all the pro- 

 perties of silica : it weighed 3'5 grains. There can therefore, 

 I think, be little doubt that at the high temperature to which 

 it was exposed, platinum took up as much as 3 per cent, of 

 silica ; or, more probably, a quantity of its base equivalent to 

 that quantity of the earth, to which it owed all its change of 

 character and properties. A temperature considerably above 

 that of melting cast-iron appears to be necessary to this com- 

 bination ; which is analogous in many respects to the ab- 

 sorption of carbon by iron in the process of making steel by 

 cementation*. 



* The combination of platinum and the base of silica formed by Mr. 

 Daniell, had before been noticed by Descotils and Chenevix ; but they con- 

 sidered it to be a carburet of platinum. Boubtiugault, however, re-exa- 

 mined it, and found it to be in reality a compound of the base of silica 

 with that metal. Dcscotils and (Chenevix obtained it by heating platinum 

 with charcoal, a'j Mr. Daniell has done by heating platinum with black-lead 

 ware. Houssingault found that when the n)etal was heated with lamp-black 

 this combination was not formed. — Sec Thomson's Inorg. Chcni. vol. i. 

 p. fJOii. — Edit. 



2 M 2 



