20 



with so many conditions. Water from deep artesian wells is sometimes 

 nearly free from dissolved oxygen, and is yet of the purest possible 

 description. 



6. The Dissolved Solids are estimated by evaporating a known 

 volume of the water to dryness in a platinum dish and weighing the 

 residue. The drying of the residue is effected at loo" C. (=212° F.), 

 a temperature high enough to drive off all except chemically combined 

 water. This residue is then ignited in the dish, and the resulting ash 

 is weighed ; the loss of weight is usually stated in a separate column in 

 reportmg the analysis, although a much less value is attached to this 

 number than was the case some years ago. The loss was then supposed 

 to be essentially due to organic matter which had been burnt away, and 

 was hence thought to be a measure of the mipurity of the water 

 analyzed. Now, we know that far more importance must be attached 

 to the kind of organic matter present than to the total amount of it, 

 and since the loss on ignition gives no information on this point its 

 indications are of correspondingly small moment, liesides this, the 

 loss is partly due to escape of carbonic acid gas from carbonates, and 

 to loss of water which has been combined in such a way that it was not 

 driven off by heating to 100° C. 



I may here mention that it is possible to burn away the organic 

 matter from the residue in such a way as to collect the products of 

 combustion, and from them to calculate the amounts of carbon and 

 nitrogen which the residue contained. Since nitrogen is, as a rule, 

 present to a larger amount in organic matter having an animal origin 

 than in that having a vegetable origin, it is possible from the relative 

 amounts of nitrogen and carbon to get an idea of the proportion of 

 animal impurities existing in the sample analyzed. This process is a 

 very tedious and troublesome one, and requires the utmost care in its 

 execution that results of any value may be obtained. It was employed 

 by Dr. Frankland in the analysis of the waters of Great Britain (1868 — 

 1876), and he concludes that surface water or river water containing 

 2 parts of organic carbon, or 0.3 parts of organic nitrogen per million, 

 should be rejected where possible. I have not employed the process in 

 the analyses ot Canadian river and well waters which T have made within 



