THE LIFE OF KARL WILHELM SCHEELE XXV11 



into the receiver carried with it a great portion of the colour- 

 ing principle, viz. prussic acid, now termed in modern chemical 

 nomenclature hydrocyanic acid or hydric cyanide. Scheele 

 thus demonstrated that Prussian blue could not be formed 

 without the intervention of this yellow prussiate, and that the 

 active principle of yellow prussiate was a substance of the 

 nature of an acid (prussic acid). He not only demonstrated 

 the composition of this acid, and described its properties and 

 compounds, but mentions its smell, and not only its smell but 

 even its taste ! Its deadly nature was happily or unhappily 

 quite unknown, and his escape from being poisoned is quite 

 miraculous. 



The speculations into which Scheele enters during his 

 investigations into Prussian blue and the experiments by 

 which he supports them are highly interesting. His con- 

 clusions are wonderfully sound, considering the great difficulty 

 and involved nature of the subject, and again demonstrate the 

 far-seeing and far-reaching nature of the man. Unfortunately 

 the last of the two essays on Prussian Blue was amongst his 

 last contributions to science. 



1784-85-86. Vegetable Acids. In these years Scheele 

 returned to the love of his youth, the vegetable acids, and dis- 

 covered and described four new organic acids, those now 

 known to us as citric, malic, oxalic, and gallic acids. 



The writer of this biography has looked more at the 

 practical benefits to mankind at large of Scheele's discoveries, 

 than as to whether Scheele during his lifetime supported this 

 or that theory, formed this or that conclusion. Americans, 

 like other nations, have benefited by Scheele's discoveries. 

 They flock by their thousands every year to Stratford-on- 

 Avon to visit Shakespeare's birthplace, and perhaps to shed a 

 tear over his grave, a pardonable but sentimental feeling 

 all the same for a man who, if he endowed the world with 



