Ixxviii GENERAL SUMMARY OF SCIENTIFIC AND 



De Souza lias made a series of experiments to ascertain whether 

 amalgams are actually chemical compoimcls. He maintained both 

 silver and gold amalgams at the temperature of boiling sulphur until 

 the weight remained constant, and then found that the former con- 

 tained its constituents in quantities required by the formula Agj3Hg, 

 and the latter, AUgHg, thus confirming the theory of chemical union. 



E. Dumas has written upon the touch-stone, giving an extended 

 historical sketch of the subject, and furnishing an analysis of a stone 

 w^hich has been used from very ancient times in the Paris assay 

 office. It proved to be a piece of fossil wood, of an unknown genus 

 and species, however, to which, on microscopic data, Renault assigns 

 the generic name Ohrussaxi/lon, meaning wood used for assaying gold. 



Sainte-Claire Deville and Debray have published some data con- 

 cerning the density of inwe platinum and jDure iridium prepared 

 with great care, and also that of several alloys of these metals. They 

 find that the mean density of platinum, estimated from ingots weigh- 

 ing from 200 to 250 grammes, is 21.5. Iridium in the ingot has a 

 density of 23.239 ; after breaking under the rolls, of 22,421. An al- 

 loy of 10 per cent, iridium has a density of 21.615 ; of 15, 21.618 ; of 

 33.33,21.874; of 95, 22.384. 



Scheurer-Kestner has communicated additional facts upon the 

 corrosion of platinum stills which are used for the concentration of 

 sulphuric acid. He finds (1) that the loss is not mechanical but 

 chemical, the metal being contained in the acid in solution ; (2) that 

 when the acid is free from nitrous compounds, it dissolves about 

 one gramme of platinum for every ton of sulphuric acid concen- 

 trated to 93-94 per cent., but six to seven grammes per ton when 

 the concentration is pushed to 98 and above, rising even to nine 

 grammes when the acid marks 99|- per cent. ; (3) that the loss is 

 even more considerable if nitrous products are present in the acid, 



Boussingault has published a memoir upon the silicification of 

 l^latiuum and some other metals, showing that they do not unite 

 with carbon at a red heat, that carbon reduces silicon at a high tem- 

 perature, that platinum heated to whiteness in a silicious carbon 

 crucible is silicified, and that the silicon is held by the carbonous 

 oxide. 



E. von Meyer has studied at length the apparent action of chem- 

 ical attractions called into play during the slow oxidation of hydro- 

 gen and carbonous oxide by means of platinum. 



Deville and Debray have observed that cyanide of potassium 

 mixed with spongy platinum, and heated to 500 or 600 Centigrade 

 in presence of aqueous vapor, evolves liydrogen, and forms potassio- 

 platinum cyanide. The same is true of a concentrated solution of 

 the cyanide. The authors show that this result flows necessarily 

 from the thermal exchanges involved in the reaction. 



Zarawkowitch proposes the use of glycerin for reducing platinum 



