XXVI THE LIFE OF KARL WILHELM SCHEELE 



1783. Glycerin.- In 1783 he discovered glycerin, the 

 sweet principle of oils. Next to chlorine, this was perhaps 

 his most important discovery, and his description of it given 

 in the Essays will well repay perusal by chemists of the 

 present day. Here again a student of chemistry commencing 

 the study of oils and fats could not do better than repeat 

 the experiments by which Scheele obtained glycerin. The 

 minor uses of glycerin are legion, it would take more than a 

 page of this volume to even enumerate them ; many of them 

 are no doubt familiar to the reader, the glycerin barometer 

 for example. Of the use of glycerin on the large scale we need 

 only refer to the enormous consumption of it in the manu- 

 facture of that formidable reagent nitroglycerin, which, when 

 reduced with infusorial earth, forms the more safe dynamite. 



178283. Prussian Blue, Prussic Acid. Nothing could 

 be more difficult than to apportionate, with some degree of 

 accuracy, its relative importance to each of Scheele's investiga- 

 tions ; we shall be content, therefore, to remark that perhaps 

 of all his experimental researches this is the one which 

 displays Scheele and his remarkable genius at its very best. 

 He passes from experiment to experiment with the most 

 astonishing agility and facility. The object which he 

 had in view was to discover the colouring principle of that 

 pigment, and that object he never lost sight of throughout. 

 He first of all demonstrates that the salt produced by digest- 

 ing Prussian blue in caustic potash was a triple compound of 

 (a) the colouring principle (&) iron and (c) potash, viz., what is 

 known at the present day as yellow prussiate of potash or 

 potassic ferrocyanide, the iron being, as he imagined, the 

 medium link or bond by which the colouring principle is 

 attached to the alkali. This salt, viz. the yellow prussiate, he 

 decomposed by distilling its aqueous solution with a small 

 quantity of vitriolic acid, and the liquid which passed over 



