Intelligence and Miscellaneous Articles. 229 



cess for forming it, and which is given as follows in the An- 

 nates de Chimie for April last. In giving it, it is to be ob- 

 served that M. Guimet expresses a doubt whether it will yield the 

 colour at a sufficiently cheap rate; but M. Gmelin asserts that 

 it succeeds infallibly : — Prepare hydrate of silica and hydrate of 

 alumina; the former is obtained by fusing well-powdered quartz 

 with four times its weight of carbonate of potash, dissolving the 

 fused mass in water, and precipitating by muriatic acid; hydrate 

 of alumina is procured by precipitating a solution of alum with am- 

 monia. These two earths are to be carefully washed with distilled 

 water. After this, the quantity of dry earth remaining is to be as- 

 certained, by heating to redness a certain quantity of the moist 

 precipitates. The hydrate of silica which 1 employed in my expe- 

 riments, contained in 100 parts 56, and the hydrate of alumina 3*24 

 parts of anhydrous earth. 



Dissolve afterwards, with the assistance of heat, as much of this 

 hydrate of silica as a solution of caustic soda is capable of taking 

 up, and determine the quantity dissolved. Take then for 72 parts 

 of the latter (anhydrous silica), a quantity of hydrate of alumina, 

 which contains 70 of anhydrous alumina; it is to be added to the so- 

 lution of silica, and the mixture is to be evaporated, with constant 

 stirring, until a moist powder only remains. 



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

 ultramarine, which is to be coloured by sulphuret of sodium ; and 

 this is effected in the following manner : — Put into a Hessian cruci- 

 ble, provided with a good cover, a mixture of two parts of sulphur, 

 and one part of anhydrous carbonate of soda ; it is to be gradually 

 heated, until at a moderate red heat the mass is well-fused : this 

 mixture is then to be projected, in very small quantities at a time, 

 into the middle of the fused mass; as soon as the effervescence, oc- 

 casioned by the vapour of water, ceases, a fresh portion is to be 

 thrown in. Having kept the crucible moderately red-hot for an 

 hour, it is to be taken from the fire and suffered to cool. — It now 

 contains ultramarine, mixed with sulphuret in excess, which is to 

 be separated by water. If there be sulphur in excess, it is to be 

 expelled by a moderate heat. If the whole of the ultramarine be 

 not equally coloured, the finer parts may be separated, after having 

 reduced them to a very fine powder, by washing with water. — Ibid. 

 April 1828. 



MELLITIC ACID. 



M. Woehler makes the following statement as to the means of 

 obtaining this acid. I boil the mellite (mellitate of alumina) re- 

 duced to fine powder with subcarbonate of ammonia, and crystallize 

 the resulting mellitate of ammonia. This salt is dissolved and pre- 

 cipitated by acetate of lead, and the precipitate is decomposed by 

 sulphuretted hydrogen. Filter and evaporate to the consistence of 

 a syrup ; crystallization occurs with difficulty, but a white mass is 

 obtained. This is to be dissolved in cold alcohol, and the solution 

 by spontaneous evaporation, yields groups of stelliform crystals ; 

 these crystals have a strong acid taste, are unalterable in the air, 



and 



