Chemical Science. 217 



of carbonate of soda, the mass dissolved in water, and then preci- 

 pated by muriatic acid ; thus a hydrate of silica will be formed. A 

 hydrate of alumina is to be prepared by precipitating alum by 

 ammonia. These two earths are to be carefully washed with 

 boiling water ; the proportion of dry earth in each is then to be 

 ascertained by heating a small quantity and weighing it. The 

 hydrate of silica used by M. GmeHn contained 56 per cent., and the 

 hydrate of alumina 3.24 per cent. 



As much hydrate of silica is then to be dissolved in a hot solution 

 of caustic soda as it will take up, and the quantity determined ; then 

 such proportion is to be taken as contains 72 parts of anhydrous 

 silica and a quantity of the hydrate of alumina, equivalent to 70 

 parts of dry alumina added to it, and the whole evaporated toge- 

 ther, being continually stirred, until it becomes a damp powder. 



This combination of silica, alumina, and soda, is the basis of 

 ultramarine, and is now to be coloured by a sulphuret of sodium in 

 the following manner. A mixture of 2 parts of sulphur with 1 part 

 of anhydrous carbonate of soda is to be put into a Hessian crucible, 

 covered up, and then gradually raised to a red heat until it is well 

 fused ; then the mixture is to be thrown in very small quantities at 

 a time into the midst of the fused mass. As soon as the effer- 

 vescence occasioned by the water in one portion has ceased, ano- 

 ther portion is to be added. Having retained the crucible at a 

 moderate red heat for an hour, it is to be removed from the fire 

 and allowed to cool. It now contains ultramarine, mixed with 

 excess of sulphuret : the latter may be separated by water. If 

 sulphur is in excess, a moderate heat will dissipate it. If all the 

 parts are not equally coloured, a selection should be made, and then 

 the substance reduced to fine powder. — A?in. de Chimiey xxxvii. 409. 



33. On an economical Method of dissolving Metals in Acids in the 

 Manufacture of certain Metallic Salts, by M. Berard. — The method 

 which M. Berard describes is founded upon the rapid effect of ox- 

 idation which takes place when certain metals are exposed to air 

 and moisture, or air and acids at the same time. These effects have 

 long been known, but have not been hitherto applied : ordinarily, 

 when me'.als are to be dissolved in acids, they are oxidized in the 

 first place by air and heat, or else are converted into oxides during 

 the act of solution, at the expense of the water or the acids, and the 

 processes are often inconvenient and expensive. 



M. Berard's method consists in granulating or laminating the 

 metal, then putting it into vessels, so as to expose as much surface 

 to air as possible ; afterwards filling the vessels with the acid in 

 which the solution is to be effected, which acid must be diluted; 

 then withdrawing the acid, and leaving the moistened metal in con- 

 tact with the air. The oxidation proceeds with such energy that 

 much heat is generally evolved. After 10 or 12 hours, the acid is 

 pgain put upon the metjil, anc[ being left for an hour or two readily 



