CH. II THE ACIDS 13 



regarded as the basis of the modern science of " Organic 

 Chemistry." Amongst the acids discovered by Scheele were 

 TARTARIC ACID prepared in 1770 from " tartar," in which it 

 is present in combination with potash ; BENZOIC ACID from 

 benzoin (1775); URIC ACID from bladder-stones (1776); 

 LACTIC ACID from sour milk (1780) ; OXALIC ACID by the 

 action of nitric acid on oils (1783); CITRIC ACID from 

 lemon-juice (1784); and MALIC ACID from apples (1786). 



Oil of vitriol, or sulphuric acid. A great advance was 

 made by the discovery in the early alchemistic period of 

 powerful acids of mineral origin. The first of these to be 

 prepared was undoubtedly oil of vitriol, which the writings 

 of Geber (800 A.D.) describe as obtained by the distillation 

 of alum. The acid can be prepared more easily by distil- 

 ling green vitriol, as described in the writings of Basil 

 Valentine and of Glauber, and it was from this method of 

 preparation that the acid obtained the name OIL OF VITRIOL. 

 The first stage of distillation results in the formation of clouds 

 of steam : subsequently, dense white fumes are produced, 

 which dissolve in the condensed steam to form oil of vitriol. 

 When the white fumes are condensed separately, a strongly 

 fuming liquid is produced which hisses violently when poured 

 into water : this fuming liquid is often called NORDHAUSEN 

 OIL OF VITRIOL from the name of the German town in which 

 it used to be manufactured. The red, rusty residue remaining 

 behind in the retort was known as COLCOTHAR, and is now 

 sold as ROUGE. This method of making oil of vitriol is 

 described by Basil Valentine as follows : 



" If you get such deep graduated and well prepared 

 Mineral, called Vitriol, then pray to God for understanding 

 and wisdom for your intention aqd after you have calcined 

 it, put it into a well coated Retort, drive it gently at first, then 

 increase the fire, there comes in the form of a white spirit of 

 vitriol in the manner of a horrid fume, or wind, and cometh 

 into the Receiver as long as it hath any such material in it." 

 (Last Will and Testament, p. 158.) 



