1814.] Mr. Scheele. 167 



fight of oxygen and a smaller quantity of phlogiston. To attempt 

 a bare enumeration of all the curious discoveries contained in this 

 small volume would he out of the question. I shall just notice some 

 of the most remarkable. When black oxide of manganese is 

 exposed to a red heat, or heated with sulphuric acid, it gives out a 

 species of air the properties of which are described. Scheele calls 

 it empyreal air. It is the substance now well known under the 

 name of oxi/^en sa.i, and had been discovered three years before 

 the publication of Seheele's work by Dr. Priestley. Atmospherical 

 air is composed of oxygen gas and another air, the properties of 

 which are described. It is the gas now well known under the name 

 of azote. Combustion deprives air of its oxygen ; so do the sul- 

 phurets, and a mixture of iron filings and sulphur. The metallic 

 oxides, when reduced, give out oxygen gas. In short, the proper- 

 ties of oxygen gas, and its action on different substances, are 

 described with so much minuteness, and general accuracy, that this 

 work must h:ive furnished Lavoisier with the greatest part of the 

 facts which he employed in establishing his system. The experi- 

 ments on nitrous gas, sulphureted hydrogen gas, fulminating gold, 

 pyrophoru*, are no less curious and important : nor ought 1 to omit 

 mentioning the curious facts ascertained respecting the action of the 

 prismatic rays on the muriate of silver, and respecting the radiation 

 of heat. In short, this book contains a complete theory of chemis- 

 try, such as Scheele had deduced it from his experiments. The 

 extreme simplicity of his apparatus, and the consequent mistakes 

 into which he fell in some materia! points, prevented his deductions 

 from being so accurate as might have been expected from so careful 

 an experimenter as Scheele. The theory was in consequence erro- 

 neous ; but the materials of which it was composed are entitled to 

 our highest admiration, and probably could not have been put 

 together by any other man than Scheele. 



10. Neither Ids dissertation on a new method of procuring 

 calomel, nor that on a new method of procuring powder of algaroth, 

 both published in 177&> ' s entitled to particular attention. They 

 describe processes which were probably useful to the apothecary, 

 but which contributed little to the improvement of the science. 



11. Hut his paper On Molybdena, published likewise in 1 778, . 

 was another master-piece of chemical analysis. He points out the 

 difference between plumbago and molybdena, substances which had 

 hitherto been confounded, and shows that molybdena consist!* of 

 sulphur united to a peculiar acid, since called molybdic acid, the 

 properties of which he describes. 



1_'. The same year he published his method of preparing the 

 pigment now well known by the name of Scheele' S green, ft is an 

 arsenite of copper, and was formed by precipitating sulphate of 

 copper by arsenite of potash. 



13. During the whole of the year 177^ he continued a set of 

 experiments in order to determine the proportion of oxygen gas in 

 the atmosphere. His method was to deprive a certain portion of the 



