19 



has been very greatly improved in this respect. The brownish tint of 

 the Ottawa river water, in common with many other Canadian rivers, as 

 the RicheHeu, the Yamaska, etc., is due chiefly to dissolved vegetable 

 matter of peaty origin. Alumina has the propert) of precipitating such 

 colouring matter, hence the improvement on adding alum. In reference 

 to this feature, namely, colour in water, I may say that while it is 

 desirable on aesthetic grounds that a drinking water should be as 

 colourless as possible, we know of no positive reason for condemning a 

 highly coloured water as unwholesome. I shall show later that the pre- 

 sence of much organic matter, even though only of vegetable origin, and 

 innocent enough in its character, is cause for anxiety and possible dan- 

 ger, and of course so far as colour helps us to ascertain the presence of 

 such matter it becomes a valuable factor in the analysis ; still we must 

 remember that it is only as potentially, not as actually dangerous, that 

 we object to the use of peaty waters, and we cannot therefore condemn 

 them on the ground of high colour alone. The observation and record- 

 ing of colour in water is of greatest consequence when the same ivater 

 snpply is studied from day to day. Then indeed, a change in tint cor- 

 responds always to a change in character ; and the cause of this change 

 must be looked for, if necessary, by a complete analysis of the water. 

 For purposes of registering the observed depth of colour nothing better 

 is known to me than the scale devised by 1 ovibond, in which a set of 

 glass slips of fixed and comparable colour values is employed. I am 

 able to shew you the standard glasses, but a full illustration of the mode 

 of using them would require more time than we have to spare. The 

 depth of colour is expressed in terms of this scale in Bulletins 15 and 

 18 of the Inland Revenue Department. 



4. Turbidity and Clearness are due to matter in suspension or its 

 absence, and vary according to conditions which have already been 

 explained. 



5. Oxygeti in Solution becomes a valuable factor in the analysis of 

 the water of the same stream at different points of its course, as I have 

 already illustrated in the case of the Seine at and below Pans. The 

 estimation is, however, of no value when a single sample is concerned> 

 since the amount which may be present in a perfectly pure water varies 



