10 



mately equal degree of fineness. I will now add to each flask une 

 pint of pure water at the ordinary temperature and set them aside for 

 about half an hour. The salts I have selected are ist, Nitrate of Am- 

 monia, a proximate form taken by much of the decaying animal matter 

 on the earth's surface. This salt will be found to dissolve with extreme 

 readiness, — 2nd, Common Salt, or Chloride of Sodium, which exists in 

 vast stratified deposits on every continent and is brought to the surface 

 by natural agencies, such as mineral springs, or artificially by pumped 

 wells (as in the St. Clair Flats, at Goderich, Seatorth, etc.), or by mining 

 as at Cracow and elsewhere. This salt forms the most universal condi- 

 ment and anti-putrescent agent in the preservation of human food, and 

 as a consequence is present in all sewage, forming a most important clue 

 to the identification of sewage and the tracing of its course where it 

 enters rivers or lakes. Although quite soluble, this salt dissolves only 

 to about one-sixth the amount of the last named. 3rd. Epsom Salts, 

 or Sulphate of Magnesia, and 4th. Glauber's Salt, or Sulphate of Soda, 

 two substances which are very extensively found in mineral waters, and, 

 in I fact, give their cathartic properties to most medicinal springs and 

 wells. Epsom Salts dissolves to about the same extent as common 

 salt, while Glauber's Salt has only half this degree of solubility. 5th. 

 AVashing Soda, or Carbonate of Soda, and 6th. Bi-carbonate of soda, or 

 Baking Soda, which occur — especially the latter — in many effervescing 

 mineral waters, as in the Vichy and Apollinaris waters, although they 

 are of very much greater importance as manufactured salts. Washing 

 Soda is practically of equal solubility with Glauber's Salt, while bi-car- 

 bonate of soda is much less soluble. The solubility of these six salts 

 is seen to be inversely in the order in which 1 have named them. 



As illustrations of naturally occurring salts which are difificult of 

 solution, and yet dissolve to an appreciable extent in natural waters, I 

 can select no better examples than gypsum and chalk, the sulphate 

 and carbonate of lime. Five hundred parts of water are required to 

 dissolve one part of gypsum at the ordinary temperature, so that if a 

 gallon of water fully saturated with gypsum were evaporated to dryness 

 the residual gypsum would weigh only 140 grains, or less than one- 

 third of an ounce. Yet this salt occurring in natural hard waters in 

 very much less amount than is needed to saturate them, is a most 



