BACTERIA IN THE INDUSTRIES 183 



practice it is customary to use double the amount indicated by the 

 reaction. 



The caution to be observed in the use of chemical water sterilizers is 

 to mix them thoroughly into the water and allow them sufficient time to 

 act, at least 20 minutes. The amounts used should be adjusted to the 

 degree of contamination which is ascertained by titration. 



It must be borne in mind that filtering material, no matter what kind, 

 soon becomes clogged with accumulated sediment and rapidly developing 

 algae and fungi. The filtering material must therefore be frequently 

 renewed, in some cases every day and in no case should the interval be 

 more than five days. The analyst should make daily examinations of the 

 accumulated scum as this will convey valuable information as to the 

 impurities in the water and the efficiency of the filter. The filter, if not 

 properly attended to, may itself become a source of contamination. 

 Crenothrix forms are very apt to develop in sand filters, especially if there 

 is a deficiency in oxygen supply. 



Water supplies (ponds, small lakes) with abundant filamentous algae 

 may be treated with copper sulphate (1-1,000,000) before filtration. 

 This method met with much favor a few years ago, but has been quite 

 abandoned and forgotten recently. The copper sulphate can be placed in 

 a gunny sack, fastened to a boat, and distributed by rowing the boat about 

 until all of the chemical is dissolved, i part in 4,000,000 has given good re- 

 sults, as far as freeing the water of filamentous algae and also protozoa, is 

 concerned. After filtration no copper can be found in the water. The 

 filtering material must, of course, be renewed occasionally. 



Sedgwick and Rafter have devised, a method of making a microscopical 

 examination of water. Desirable quantities of water are run through a 

 graduated cylinder, having a sand plug at the lower open end. In place of 

 this cylinder an ordinary glass or tin funnel may be used. Place a per- 

 forated stopper (cork or rubber) at lower end, carrying bent outflow tube. 

 On top of opening in stopper place a bit of cotton or cheesecloth, followed 

 by ignited sand quartz (sands, Nos. 60, 120, 140, as may be desired). 

 On top of the sand place another bit of cotton or cheesecloth. Pour 

 through the desired volume of water (250 cc., 500 cc., 1000 cc., etc.), 

 and then mix the sand (with the cotton and cloth) in 5 or 10 cc. of 

 distilled or pure water and examine microscopically making the desired 

 counts. 



The following blank report sheet of a bacteriological examination 

 will serve to illustrate the nature of such analysis in a state or 

 municipal laboratory: 



