M. llegnault on Sulphonaphthalic Acid. 565 



few seconds the sugar is transformed into acid. The barytic salt is 

 then dissolved in water, and the acid is precipitated by means of a 

 solution of subacetate of lead, to be gradually added, in order first to 

 separate a brown colouring matter which arises during the reaction, 

 at least when operating in contact with the air. The last precipitate 

 obtained is colourless, and contains the acid in the state of subsalt j 

 it may then be separated by the usual means. 



Besides this acid, another non- volatile body is produced, which pos- 

 sesses the property of immediately reducing, when cold, the salts of 

 silver and of mercury. 



The very easy formation of an acid, by the contact of sugar of starch 

 or of grapes, with bases (M. Peligot observes), shows how proper it 

 is to avoid the employment of too much lime in the purification of 

 the beet-root juice j for although lime does not alter the sugar, it 

 acts, when in excess, upon the sugar analogous to that of grapes, into 

 which common sugar is easily converted by the influence of heat, acid, 

 or fermentation. There are therefore two difficulties to be avoided; 

 these may be apprehended at the same time, — the intervention of 

 acids which decompose the sugar intended to be extracted, and the 

 effects of the alkalies which act upon the sugar of starch resulting from 

 this decomposition. — L'Institut, AoHt t 1837. 



SULPHONAPHTHALIC ACID. 



It was first observed by Mr. Faraday*, that when concentrated sul- 

 phuric acid was made to act upon naphthalin, two acids were pro- 

 duced, forming salts with barytes which were distinguished by their 

 different solubility. Mr. Faraday considers these acids as formed by 

 the direct combination of sulphuric acid with naphthalin j this was at 

 first admitted by all chemists. More lately, and since the researches 

 of M. Mitscherlich on the action of sulphuric acid upon benzon, it has 

 been suspected that the composition of sulphonaphthalic acid might 

 be analogous to that of sulphobenzic acid, especially as the analyses of 

 Mr. Faraday and MM. Liebig and Woehler did not agree well with their 

 theoretic formula. 



M. Regnault has endeavoured to clear up this subject j he has se- 

 parately examined the action of common concentrated sulphuric acid, 

 and that of the anhydrous acid upon naphthalin: the following are some 

 of the results which he obtained. Sulphuric acid combined with one 

 atom of water formed only one acid compound, which is separable 

 from the excess of sulphuric acid by means of carbonate of barytes. 

 The sulphonaphthalate of barytes, obtained by the cooling of a hot 

 saturated solution, had the form of small crystalline tufts ; but, by 

 the spontaneous evaporation of a cold solution, it crystallizes in ag- 

 gregated small irregular tables. This salt, which had been dried at 

 356° Fahr., gave by analysis O H 14 . S* O 5 BaO; that is to say, 

 common sulphuric acid produces on naphthalin the same reaction that 

 the anhydrous acid does upon benzon. Two atoms of the hydrogen 

 of the naphthalin remove one atom of oxygen from two atoms of sul- 



* Mr. Faraday's paper on this subject will be found in Phil. Mag. First 

 Series, vol. Ixvii. p. 326. 



