168 Biographical Account of [Sept. 



air of its oxygen by means of a mixture of iron filings and flowers 

 of sulphur. The result was, that air contains always almost exactly 

 the same proportion of oxygen, and that this proportion amounts to 

 •j^, or ahout 27 per cent. I had the curiosity to repeat these expe- 

 riments many years ago, and found that the diminution of bulk 

 varied according to circumstances, sometimes amounting to 33 per 

 cent. The reason is that hydrogen is evolved, and ammonia 

 formed, at the expense of the azotic portion of the air ; so that 

 when the experiment is made in this way, the diminution is in all 

 cases greater than the proportion of oxygen contained in the air 

 examined. It was this experiment of bcheele that misled chemists 

 resperting the proportion of oxygen in common air : and when 

 Cavendish rectified the mistake, in I7&-, it was some time before 

 the requisite attention was paid to his results ; not indeed before 

 Berthollet obtained similar results in Egvpt. 



14. In 1 779 he published a curious set of experiments on the 

 decomposition of the salts having soda for a base, by means of iron 

 or quick-lime, when deposited in a cellar. He found that when a 

 plate of iron was dipped into a solution of common salt, and sus- 

 pended in a cellar, after an interval of a fortnight there was an 

 efflorescence of carbonate of soda upon the iron. The same thing 

 happened if sulphate or nitrate of soda were substituted for common 

 salt. \Mien any of these salts was mixed with quick-lime slightly 

 moistened, and left in the same situation, the same decomposition 

 took place. These curious facts have not hitherto been explained 

 in a satisfactory manner, unless we admit the effect of quantity so 

 ingeniously advanced by Berthollet in his treatise on affinity. 



15. The same year he published his experiments on plumbago, 

 in which he demonstrated that it possessed the properties of char- 

 coal, but contained about -^th of its weight of iron. 



16". His curious paper on milk made its appearance in the Me- 

 moirs of the Stockholm Academy for 1780. He ascertained the 

 chemical properties of curd, showed upon what the coagulation of 

 milk depended, and proved that it contained a new acid of a pecu- 

 liar nature, to which the name of lactic acid has been given. This 

 acid does not crystallize, cannot be distilled over, and forms deli- 

 quescent salts with all the alkaline and earthy bases The French 

 chemists endeavoured to prove that it is merelv acetic acid holding 

 some saline matter in solution. But Beizelius has shown that their 

 opinion is ill founded, and that lactic acid possesses peculiar pro- 

 perties quite different from those of acetic acid. 



17. His next discovery, published likewise in 1780, was that of 

 saclactic acid, which he obtained by digesting a solution of sugar 

 of milk in nitric acid. The peculiar, nature of this acid was denied 

 at first by some German chemists ; but their proofs were quite 

 insufficient to overturn the accurate experimental conclusions of 

 Scheele. 



18. Scheele's memoir on tungsten was published in the Memoirs 

 of the Stockholm Academy for 1 JS1 , lie showed that it was a 



