SCHEELE AND IIIS DISCOVERIES. 
219 
In the course of 1778 this wonderfully industrious man published four sepa¬ 
rate memoirs:—1. A process for preparing Calomel. 2. The preparation of 
the Oxychloride of Antimony. 3. The preparation of what is still called 
Scheele’s Green, which was obtained on pouring a solution of Potash and white 
Arsenic in a solution of Sulphate of Copper. It is an Arsenite of Copper. 
4. Molybdenum, whose ore was originally confounded with Plumbago, Scheele 
proved that it was a compound of Sulphur and a whitish powder (Molybdic 
Acid), from which more recently Hielm extracted Molybdenum in a state of 
Metal. In 1779 he continued the same subject, and showed in what manner 
Plumbago differed from Molybdic Acid, demonstrating that it was composed of 
fixed air and Carburet of Iron. This analysis was followed by Experiments 
on the (/ucintitij of pure air contained in the atmosphere. For a year lie con¬ 
tinued his observations and obtained the same results as Lavoisier, namely, that 
pure air (Oxygen) formed -^rd part of our atmosphere. About the same time 
appeared his 4 Experiments on the Decomposition of Neutral Salts by Quick 
Lime and Iron.’ 
In the Annals of the Academy of Stockholm are three published Memoirs 
belonging to 1780. A. Remarks on Fluor Spar, being chiefly an answer 
to objections to his previous paper. B. Examination of Milk and its Acid. 
After having stated the influence of Alkalis and Acids in determining its 
coagulation, he pointed out that caseins when calcined contained Phosphoric 
Acid and Lime. In order to obtain the Acid of Milk, he evaporated the Serum 
down to an eighth part, saturated it with quicklime, which he afterwards 
separated by Oxalic Acid ; then he treated the liquor with Alcohol, which 
dissolved the Lactic Acid without touening the Sugar of Milk. On dis¬ 
tilling the Alcohol he obtained pure Lactic Acid. C. The examination of 
Sugar of Milk. On treating the concentrated Serum with Nitric Acid he 
obtained Saccho-lactic Acid in crystals, or in the form of a white powder, 
sparingly soluble in water, and forming, with alkalis, crystallizable salts. Each 
succeeding year is the record of some new and original observation; but we 
must not linger too long over details. 
In 1781 appeared the Memoir on Tungsten and his discovery of Tungstic 
Acid. In 1782 three new memoirs saw the light, the first being Observations 
on Ether , and the second, A Method for Preserving Vinegar; the third, same 
date, is an Essay on the Colouring Matter of Prussian Blue. This is one of his 
most important dissertations, and probably his chef-d'oeuvre. It is divided into 
two parts. In the first, Scheele endeavours to discover the substance which, in 
Prussian Blue, is united with Iron and an alkali. The methods employed iu 
this research are most ingenious, and show the utmost skill in the employment 
of reagents. By dint of repeated trial, he succeeded in discovering the colour¬ 
ing matter ; his first description of it being that it possessed a peculiar odour, 
that of bitter almonds ; that it had a burning taste, and produced coughing. 
It is strange that he did not at the same time remark its poisonous qualities. 
Possibly his very manipulations tended to shorten his life. In order to assure 
himself of its composition, he treated it successively with all the known alkalis 
and acids. When found, he called it simply The Colouring Matter. Bergmann 
gave it the more ambitious title of Acidum ccerulei Berolinensis , afterwards styled 
Prussic Acid by Guyton de Morveau, and finally Hydrocyanic Acid by Gay- 
Lussac. These experiments were subsequently followed up, Scheele continuing 
to study the action of this colouring matter on alkalis, acids, and metals. 
He established that Prussiate of Ammonia might be entirely sublimed ; that 
that of lime yielded its base to caustic alkalis and acids; that the colouring 
matter was capable of distillation. This product was used as a test for the 
presence of iron, and he then designated it as Precipant Liquor. In attempt¬ 
ing the elementary analysis of Prussic Acid he at first supposed that it was 
