240 MODERN SCIENCE READER 



that had betore this discovery appeared mysterious sud- 

 denly became clear, and every one engaged in chemical 

 work was helped in many ways. If it is not enough for 

 us simply to gain a clearer insight into the processes around 

 us, if we must insist upon more tangible reward, no doubt 

 it could be shown that the discovery of oxygen has con- 

 tributed largely to the material welfare of mankind not 

 directly perhaps, but by enlarging our knowledge of chem- 

 istry, so that it may be said that most discoveries made 

 since 1774 have been in a way consequences .of the dis- 

 covery of oxygen. Indirect results are often of more value 

 than direct ones. 



But there is another discovery of Scheele's that illus- 

 trates in another way that a discovery which when made 

 appears of little or no practical value, may eventually 

 prove of immense practical value and become the basis of 

 a great industry. This is the discovery of chlorine. 

 Among the many substances examined by Scheele was one 

 that is commonly known as black oxide of manganese. This 

 occurs in nature in large quantity and has long been of 

 interest to chemists. Scheele treated this with about every- 

 thing he could lay his hands on, as was his way. When 

 muriatic acid, or, as it was called by the older chemists, 

 the spirit of salt, was poured on the black oxide of manga- 

 nese, he noticed that something unusual took place. He 

 soon became aware that a colored gas was given off, and that 

 this gas had other properties besides that of color. It 

 affected his eyes, nose, throat and lungs in most disagree- 

 able ways. Many of those before me have had the exper- 

 ience of inhaling a little of this gas. I hope no one has 

 inhaled much of it. It is one of the most disagreeable 

 things chemists and students of chemistry have to deal 

 with. And it is not only disagreeable, it is extremely 

 poisonous. But Scheele did not stop his work because it 

 involved discomfort and even danger. He persisted and 

 carried it to a successful issue, and when he stopped he 

 was able to give as satisfactory an account of the now 



