^Q ON THE PURITY OF THE FIXED ALKALIS. 



quantity of potash purified by means of alcohol, ofTers tills 

 result as a term of comparison, and as a standard of the 

 greatest possible purity of potash. This however would 

 give a very erroneous computation of the quantity of real 

 alkali, as it appears, that the potash taken as a standard 

 contains only 0'73 of its weight of pure potash. 

 and a'^ccrtaiii- It is more especially in determining tlie proportion of the 

 iiig ihacom- constituent principles of salts, that this source of errour is 



poner.t parts „ ., . , , ,. i i • , ■ » 



of sdlis. to be carefully avoided ; for we know how important a good 



solution of this problem would be, and how great the diffi- 

 cuhits are, that have hitherto prevented our attaining it. 

 Mr. Berthol!et,in his inquiries into the laws of affinity, ap- 

 plying new methods of experlmeiiling to this question, ex- 

 amined those employed by llichter and Kirwan in their 

 labours on the same s;u!»ject. He found, that Kirwan, be- 

 side the number of estimations he was obliged to make, had 

 set out with a principle of too little accuracy ; and to this he 

 ascribed much of the uncertainty of the results this chemist 

 Kirwan's ine obtained. Yet Kirwan, by employing solutions of subcar- 

 of ihcsubcar- bonate of potash and of soda, to ascertain the proportions of 

 objecUoaaWe. ^^^^ ^'^^^^ *^^'^^ '"'^^^ these alkalis for their base, had only to 

 apprehend the slight errour inseparable from every such 

 analysis : and if the determination of the quantities of acid 

 employed to saturate these carbonates had been founded on 

 more certain data, the results of his experiments would have 

 been much nearer the truth. 

 Ecithollet cia- Mr. Berthollet took a more direct method, and the nature 



ployed the of the muriatic acid he employed, being better ascertained, 



murianc acid , i , ■ i • ,. , 



and ])ure al- would have led him to accurate results, il the quantity ot^ 



'^'''> water, which the muriatic acid gas probably retains, could" 



have been determined; and if he had taken, like Kirwan, 

 the alkaline carbonates as'the basis of his labours. 



It appears to me, that the preference given to potash and 

 soda prepared with alcohol has introduced into these delicate 

 experiments a source of errour, which is so much the greater 

 lis it apjdies to the substances that predominate in the com- 

 pounds, the proportions of which were to be ascertained. 

 Mr. Berthollet establishes it as a principle, that 100 parts of 

 potash prepared with alcohol, and kept in fusion for a 

 quarter of an hour, require Crs of muriatic acid to neu- 

 tralise 



