TOL. LXXI.] PHILOSOPHICAL TRANSACTIONS. \J 



before, in nitre and digestive salt. I found the salts, resulting from the satura- 

 tion of the same oil of tartar, with portions of oil of vitriol of different specific 

 gravities, to weigh, at a medium, 12.45 gr. Of this weight, only 11.85gr. 

 were alkali and acid, the remainder therefore was water, viz. 0.6 of a grain; 

 consequently 100 gr. of perfectly dry tartar vitriolate contain 28.51 gr. acid, 4.82 

 of water, and 6667 of fixed vegetable alkali. In drying this salt I used a heat 

 of 240° to expel the adhering acid more thoroughly, and I kept it in that heat a 

 quarter of an hour. 



According to Mr. Homberg, 1 French oz. (or 472.5 gr. troy) of dry salt of 

 tartar required 297.5 gr. troy of oil of vitriol, whose specific gravity was I.674, 

 to saturate it; but, by my calculation, this quantity of fixed alkali would require 

 325 gr. : a difference which, considering our different methods of determining 

 the specific gravity of liquids (his method, viz. that by mensuration, giving it 

 always less than mine) the different desiccation of our alkalis, &c. may pass 

 for inconsiderable. 



The resulting salt weighed, according to Mr. Homberg, 182 gr. Troy above 



the original weight of the fixed alkali ; but by my experiment it should weigh 



but 87.7 gr. more; for 10.5 : 12.45 :: 472.5 : 560.2. It is bard to say how 



Mr. Homberg could find this great excess of weight both in nitre and tartar 



vitriolate, unless he meant by the original weight of the salt of tartar the weight 



of the mere alkaline part, distinct from the fixed air it contained : and indeed 



one would be apt to think he did make this distinction ; for in that case the 



excess of weight will be very nearly such as he determined it : for 10.5 : 8.3 :: 



472.5 : 373.3. Now the whole weight of his nitre was 56o.2,as above shown; 



then 560.2 — 373.3 = 11 6.9, which is only 4 gr. more than he determined it. 



Hence he inferred, that 1 oz. (472.5 gr. Troy) of this oil of vitriol contains 



291.7 gr. of acid. By my computation it contains but 213.3 ; but it must be 



considered that he made no allowance for the water contained in tartar vitriolate, 



and imagined the whole of tne increase of weight proceeded from the acid that 



is united in it to the fixed alkali. Now the aqueous part in o6o gr. of tartar 



vitriolate amounts to 37 gr. the remaining difference may be attributed to the 



different degrees of desiccation, &c. 



Of the acetous acid. — I have made no experiment on this acid ; but, by 

 calculating from the experiment of Mr. Homberg, I find the specific gravity of 

 the pure acetous acid, free from superfluous water, should be 2.130. It is pro- 

 bable that its affinity to water is not strong enough to cause any irregular increase 

 in its density, at least that can be expressed by 3 decimals ; and hence its pro- 

 portion of acid and water may always be calculated from its specific gravity and 

 absolute weight. 100 parts of foliated tartar, or, as it should rather be called, 

 acetous tartar, contain well dried 32 of fixed alkali, .19 of acid, and 49 parts of 

 vol xv. D 



