626 Boussingault's experiments on the action of [Dec. 



In the process of cementation, it was evident that the silver was 

 converted into a chloride by the action of dry clay and dry salt. 

 Boussingault commenced his inquiries with precisely the same mate- 

 rials, operating on fine gold dust, containing 26 per cent, of silver, <md 

 substituting only well baked Cornwall crucibles for the fragile porous 

 ware of the country : — he was surprised however to find that no action 

 whatever now took place, although he maintained his fire for 72 

 hours ! and to the exultation of the natives he was forced to allow 

 the superiority of their old and despised methods. 



To ascertain whether air was necessary to ensure success, one slip of 

 silver, weighing 24.6 grs., was cemented in a well-closed crucible, 

 covered with charcoal powder ; while another of the same size was 

 merely encased in cement, without a crucible, so as to favor the access 

 of air. After seven hours, the former had lost only 0.3 gr., while the 

 latterwas reduced in weight to 9.5 grs. The presence of air was thus 

 proved to be indispensable : it remained to examine in what way it 

 acted. Salt by itself may be fuzed and sublimed in an open silver 

 crucible, without acting upon it in any degree — the volatilization is 

 materially accelerated by a current of hot air, but without any danger 

 of affecting the metal. 



Two slips of silver were again prepared, weighing 6.5 : one was 

 cemented with a mixture of pure silex and salt; the other with pure 

 alumina and salt. After four hours, under a muffle at a cherry-red 

 heat, the latter had entirely disappeared ; the cement was slightly 

 agglutinated, crystalline, and no longer saline to the taste. The other 

 slip still weighed 4 grs. ; its surface was remarkably crystallized, and 

 covered with a green glass, which adhered strongly. The cement was 

 also completely vitrified, to which circumstance doubtless the bad 

 success of the cementation was attributable. 



It is known that pure silex has no action whatever on salt when 

 both are dry, but the moment aqueous vapour is introduced, a powerful 

 re-action commences, muriatic acid is disengaged, and silicate of soda 

 remains. In the above experiments then water must have got to the 

 cement even through the heated muffle of the furnace, and it occurred 

 that the success of the Santa Fe cementation might be mainly attribu- 

 table to the quantity of wet vapours necessarily formed in the combus- 

 tion of a wood-fire. 



To prove whether it was the water contained in the atmosphere, or 

 that supplied by the fuel, that favored the process, Boussingault 

 placed a slip of silver, coated with the cement, in a porcelain tube, 

 heated red, through which he then passed a current of dry air ; — the 

 silver remained untouched. 



