396 KANSAS CITY REVIEW OF SCIENCE. 



Test for copper. — Immerse a polished plate of iron in the water to be ex- 

 amined, and let it remain for a few minutes. If copper be present, the plate of 

 iron will be coated over with copper, A few drops of ammonia solution will 

 turn water containing copper a dark blue color. 



For all domestic purposes soft water should be preferred, and that which is 

 clear and with little or no taste. But mineral water (water in which mineral mat- 

 ter is dissolved) is less dangerous than that in which organic and animal matter is- 

 contained, as this is the common source of most of our infection diseases — typhus^ 

 scarlet-fever, etc. One of the readiest and simplest tests for ascertaining if water 

 is free from organic pollution is to cork up a small bottle nearly full of it, in 

 which a piece of lump sugar has been put. If, by thus excluding the air and 

 letting it stand in the light for two or three day, there is not a milky cloud, but 

 the water remains clear, it may be considered free from the phosphates which 

 are always present in sewage water. — Boston Journal of Commerce. 



CONCERNING FLUORINE. 



It was known nearly two hundred years ago that glass could be etched by- 

 exposing it to the fumes produced by the action of sulphuric acid on the min- 

 eral called fluor-spar ; but it was not until the present century that the nature of 

 the chemical reaction in the process was understood. Until the time of Ampere's- 

 investigations, in 1810, it was supposed that the acid attacking the glass was an 

 oxygen compound; but that chemist showed, as Davy subsequently did, that the 

 acid was analogous to hydrochloric acid, being a compound of hydrogen with an 

 element existing in the fluor-spar in combination with calcium. This element 

 was named fluorine, and the fluor-spar, formerly known as fluate of lime, was- 

 designated as fluoride of calcium. 



This fluorine is interesting from the fact that (setting aside certain "new 

 metals" whose oxides have been "discovered" within the last few years, but 

 whose existence is still hypothetical) it is the only element that has not been iso- 

 lated. Many attempts have been made to obtain it in its simple form, but with- 

 out success. 



It is easy enough to decompose its compounds, but impossible to prevent it 

 from immediately entering into new ones. It attacks glass and the metals, so 

 that the chemist is at a loss to find a material for vessels in which to prepare or 

 confine it. It unites at once with platinum, which is proof against so many- 

 chemical agents. Davy heated dry fluoride of silver with chlorine gas in a plati- 

 num vessel, and got for his pains a fluoride of platinum. He tried the same ex- 

 periment in a glass tube, and obtained chloride of silver, but the released fluorine 

 attacked the glass, entering into combination with its silicon. For this latter ele- 

 ment it has an extraordinary affinity, and its action upon glass is due to this fact. 

 Glass is a siHcate, or a compound of silicic acid with soda, lime and other metallic 

 oxides. The fluorine decomposes the silicic acid (SiOj), and forms with the 



