Tassaert on Chr ornate of Potassa. 311 



the neutral chromate of potash is a subsalt, for repeated washings 

 and crj'Stallizations do not deprive it of the property of restor- 

 ing the blue colour to reddened litmus paper. In attempting 

 to form the neutral chromate, he found that, when he employed 

 a solution of chromate containing nitre, even in small quantity, 

 this could be easily separated by adding to the liquors an excess 

 of alkali. On subsequent concentration, the whole of the nitre 

 crystallized in well-formed prisms, carrying down with it but a 

 small quantity of chromate ; whilst if we saturate first of all 

 the solution of chromate, so as to make it neutral, and after- 

 wards evaporate, since the salt thus formed and the nitre have 

 nearly the same degree of solubility, they fall down together 

 in crystals, and can no longer be separated : but the contrary 

 takes place when the neutral chromate is converted into a sub- 

 salt, it thus becomes much more soluble, and lets the nitre 

 form first. 



This difference of solubility between the acid chromate and 

 the subchromate of potash, is very well marked; for if into a 

 saturated or nearly saturated solution of alkaline chromate, we 

 pour some drops of acid, there is immediately formed an abun- 

 dant deposit of acid chromate. To free the salt completely 

 from nitre, he recommends it to be deflagrated with charcoal in 

 a crucible ; and afterwards to be dissolved, filtered, and crys- 

 tallized. M. Tassaert analyzed the chromates of potash, by 

 drying them for several days in a temperature of from 50° to 

 60° C, precipitating their acid by acetate ot barytes, washbg 

 the barytic salt, and adding to the supernatant liquid, sulphuric 

 acid in excess; evaporating and igniting the sulphate of potash. 

 He thus found that the acid chromate, which is naturally 

 formed in the neutral solution, is composed of 



Chromic acid .... 67.40 

 Potash 32,60 



while the alkaline salt consists of 



Chromic acid 52.0 



Potash 48.0 



It is to be observed, that chromate of barytes begins to dissolve 

 in water, the moment that we remove from it the whole of the 

 acetate of barytes that it contains mixed with it : it then dis- 

 solves in sufficient quantity to colour yellow the filtered liquors. 

 A single drop of acetate of barytes, mixed with the edulcorat- 

 ing water, stops the dissolving process, and renders the filtered 

 liquid turbid. Water, with a little alcohol, equally prevents 

 this solution. — Ann. de Chim. et de Phys., xxii. 51. 



9. Analysis of different Limestones, by M. P. Berzelius, 

 Ingenieur des Mines. 

 After giving a table of analyses of French limestones, not fit 



