206 Mr, Faraday on the Mutual Action of Sulphuric Acid [Sept, 



baryta was separated, no excess of sulphuric acid being per* 

 mitted. Being filtered, a pure aqueous solution of the peculiar 

 acid was obtained. It powerfully reddened litmus paper, and 

 had a bitter acid taste. Being evaporated to a certain degree, 

 a portion of it was subjected to the continued action of heat. 

 Whenvery concentrated, it began to assume a brown colour, and> 

 on cooling, became thick, and ultimately solid, and was very 

 deliquescent. By renewed heat it melted, then began to fume', 

 charred, but did not flame ; and ultimately gave sulphuric and 

 sulphurous acid vapours, and left charcoal. 



Another portion of the unchanged strong acid solution was 

 placed over sulphuric acid in an exhausted receiver. In some 

 hours it had by concentration become a soft white solid, appa- 

 rently dry; and after a longer period was hard and brittle. In 

 this state it was deliquescent in the air, but in close vessels 

 underwent no change in several months. Its taste was bitter, 

 acid, and accompanied by an after metallic flavour, like that of 

 cupreous salts. When heated in a tube at temperatures below 

 212°, it melted without any other change, and on being allowed 

 to cool, crystaUized from centres, the whole ultimately becoming 

 solid. When more highly heated, water at first passed oflT, and 

 the acid assumed a slight red tint; but no sulphurous acid was 

 as yet produced, nor any charring occasioned ; and a portion 

 being dissolved and tested by muriate of baryta, gave but a very 

 minute trace of free sulphuric acid. In this state it was proba* 

 bly anhydrous. Further heat caused a little naphthaline to rise, 

 the red colour became deep-brown, and then a sudden action 

 commenced at the bottom of the tube, which spread over the 

 whole, and the acid became black and opaque. Continuing the 

 heat, naphthaline, sulphurous acid, and charcoal, were evolved ; 

 but even after some time the residuum, examined by water and 

 carbonate of baryta, was found to contain a portion of the pecu* 

 liar acid undecomposed, unless the temperature had been raised 

 to redness. 



These facts establish the peculiarity of this acid, and distin- 

 guish it from all others. In its solid state it is generally a 

 hydrate containing much combustible matter. It is readily 

 soluble in water and alcohol, and its solution forms neutral salts 

 with bases, all of which are soluble in water, most of them in 

 alcohol, and all combustible, leaving sulphates or sulphuretfi 

 according to circumstances. It dissolves in naphthaline, oil of 

 turpentine, and olive oil, in greater or smaller quantities, accord-*- 

 ingly as it contains less or more water. As a hydrate, when it is 

 almost insoluble in naphthaline, it resembles the heavier sub- 

 stance obtained as before described, by the action of sulphuric 

 acid on naphthaline, and which is the soHd hydrated acid, con* 

 taining a little naphthahne, and some free sulphuric acid ; whilst 

 the lighter substance is a solution of the dry acid in naphthaline; 



