The Relations between Marine Animai and Vegetable Life. 345 



standard solution could be varied at will. White liglit was reflected 

 up the tubes by means of a porcelain piate placed at an appropriate 

 angle underneath the glass piate, and the two tubes were viewed 

 from above through a mask with two cireular holes in it. The 

 amount of ammonia present could thus be determined far more readily 

 and more accurately than by the method adopted by Wanklyn and 

 Chapman, in which separate standard Solutions of various strengths 

 bave to be made up, until oue of the same degree of colouratìon as 

 the solution under examination is hit upon. After 200 ce. bave been 

 distilled off the 500 ce. of water, whereby ali the free ammonia present 

 is removed, 50 ce. of a strongly alkaline solution of potassium per- 

 manganate solution is added, and a further 150 ce. distilled off. This 

 distillate contains the so-called albumìnoid or organic ammonia present 

 in the water. It was fouud by Wanklyn and Chapman ^ that most 

 organic substances such as egg albumin, gelatin and amylamine 

 Compounds, yield, on distillation with alkaline permanganate solution, 

 the whole or a large part of the nitrogen they contain, in the form 

 of ammonia. This method therefore gives one a fair criterion of the 

 amouDt of organic impurity contained in the water. The amount of 

 free ammonia present at the same time also affbrds confirmatory 

 evidence as to the degree of contamination present. Nevertheless, the 

 method is not to be regarded as a ver}^ exact one, or as affording 

 an absolute measure of the degree of organic impurity. Thus, for 

 instance, it was found that in oue case when a specimen of water 

 was distilled 2.3 times more slowly than usuai, the amounts both 

 of free and organic ammonia were increased by some 10^. At the 

 same time the method is probably the simplest and best one available 

 for estimating the quality of a water. It was not thought worth 

 while to make other determinations, as of the amount of oxygen 

 used up on the addition of excess of dilute permanganate solution, 

 as the results thereby obtained add but little to those yielded by the 

 ammonia process. 



The bacteriological side of the investigation consisted merely 

 in making gelatin piate cultures of the various specimens of water, 

 and counting the number of colonies present after the cultures had 

 been kept 24 and 48 hours in a moist Chamber. 



This research naturally divides itself into two parts: the puri- 

 fication of water by vegetable lite, and the fouling of water by 

 animai life. The former will be dealt with first. 



» ibid. pag. 182. 



