64 SCIENTIFIC AMUSEMENTS. 



contains more or less salt, the result is that during many centuries 

 past salt has been accumulating in the lake, which is now a very 

 strong briny liquor quite undrinkable, like sea-water. In the 

 shallow parts of the lake the sun evaporates the water so quickly 

 that crystals of salt are continually forming, and sinking to the 

 bottom, forming a layer of solid salt. 



In many parts of America a similar action has gone on with lakes 

 into which streams once flowed containing other forms of saline 

 matter besides common salt ; and the dried-up beds of these lakes 

 are consequently valuable deposits of the saline matters thus left. 



The substances termed borax and nitrate of sodium (or Chili salt- 

 petre) are obtained in large quantities from sources of this de- 

 scription. 



The "mother-liquors" from whieh salt has separated by crystal- 

 lisation, obtained by evaporating down natural brine or sea- water, 

 are sometimes used medicinally, as the substances communicating 

 the bitter taste are, generally speaking, strongly purgative. " Fried- 

 richshall Wasser " (water from the spring at Friedrichshall), and 

 " Kreutznach Bittern " (bitter mother-liquors from the Kreutznach 

 spring) are fluids of this kind. The mother-liquors of the Cheshire 

 salt-works contain substances rendering them valuable for the cure 

 of rheumatism, &c., when used as baths ; and the same remark 

 applies to many other saline springs. The comparatively scarce 

 substances iodine and bromine are often contained to a considerable 

 extent (combined with other substances) in such mother-liquors, 

 which are consequently valuable as a source of these chemicals. 



Expt. 57. To separate Common Salt from other Soluble 

 Substances by Crystallisation. Take a couple of ounces of 

 common salt and dissolve it in a sufficient quantity of hot water ; 

 add to the liquid a few drops of a solution of "perchloride of 

 iron," otherwise termed ferric chloride, and also a few drops of 

 diluted hydrochloric acid. You thus obtain a compound solution 

 containing chiefly salt, but also small quantities of other soluble 

 matters. Obtain some blue litmus test-papers ; these are made by 

 soaking the substance called litmus (a colouring matter derived 

 from a vegetable substance termed the litmus lichen} in spirit, 

 so as to obtain a " tincture " thereof, i.e., a solution in alcohol of 

 those constituents soluble in that medium ; a blue or purple fluid 

 results, in which fine blotting-paper is dipped and dried. The 

 coloured paper cut into slips can be used as a test for hydrochloric 

 acid, which, like all other acids, possesses the peculiar property of 

 turning this particular blue colouring matter red, even when only 

 present in very small proportions. Consequently, if you dip a 

 blue-litmus test-paper in the compound solution prepared as above 



