289 



On Super-acid and Sab-acid Salts. By William Hyde Wollaston, 

 M.D.Sec.R.S. Read January 28, 1808. [PML Trans. 1808, 

 p. 96.] 



The author having some time since observed various instances of 

 super-acid salts, in which he found that the quantity of acid was 

 exactly double of what would be necessary merely to saturate the 

 alkali present, had intended to have pursued the inquiry, but was , 

 prevented by the publication of Mr. Dalton's theory of chemical 

 combination, as explained by Dr. Thomson. 



However, since it appeared that Mr. Dalton's theory was originally 

 founded on the analysis of gases, which is attended with too many 

 difficulties to be repeated by every one who may be desirous of veri- 

 fying the law of simple multiples by experiment, the author thought 

 it might be desirable to select from his observations certain experi- 

 ments extremely easy to be repeated, each of which exhibits in itself 

 the most direct and simple proof of the law under consideration. 



The subcarbonates of potash and of soda are named as instances 

 of salts containing exactly half the acid necessary to form their 

 fully-saturated carbonates ; and the proof is obtained by taking two 

 quantities of either of these alkalies fully carbonated. One quantity 

 being taken exactly double of the other, is exposed to a red heat, 

 and is thereby reduced to a semi-carbonate ; for it now yields the 

 same measure of gas that is given out by the unburnt half quan- 

 tity. 



Super-sulphate of potash is adduced as an instance of a salt con- 

 taining an exact double share of acid. The proof consists in taking 

 two equal quantities of potash, to one of which is added any large 

 quantity of sulphuric acid, and the mixture is exposed to a red heat, 

 by which a part of the redundant acid is expelled ; but such an ex- 

 cess of acid remains as is neutralized by the second equal portion of 

 alkali reserved for that purpose. 



Super-oxalate of potash is also proved to be an exact binoxalate. 

 Two equal quantities are taken of salt of sorrel ; one is exposed to a 

 red heat, to destroy the whole of its acid, after which the alkali that 

 remains is just sufficient to neutralize the redundant acid of the other 

 portion. 



In addition to the preceding compounds selected as distinct exam- 

 ples of semi-acid and bin-acid salts, the author has observed one re- 

 markable instance of a more extended and general prevalence of the 

 same law. For when the circumstances are such as to admit the 

 union of a further quantity of oxalic acid with potash, the quantity 

 is again doubled ; so that the potash present is sufficient to saturate 

 only one part in four of the acid contained in any quantity of the 

 salt; and, consequently, the three redundant parts of acid require 

 for their neutralization the alkali of three equal quantities of this 

 quadroxalate, which may be obtained by burning, as proof that the 

 proportion has been rightly ascertained. 



The last experiment is designed to determine whether potash would 



