WATER 29 



waters, are much mure palatable than soft water or those free 

 in 'in much gas in solution. 



Microscopical Examination. The microscopical examination of 

 water is often of great diagnostic value. The suspended matter is 

 given about twenty-four hours to become deposited at the bottom 

 of a tube and the supernatant fluid is syphoned off. Portions of 

 the sediment are then transferred to a slide and examined under 

 a low power. Hollow ground slides are more suitable than flat 

 slides. In the sediment may be found mineral matter, dead 

 vegetable matter, dead animal matter, vegetable organisms and 

 animal organisms in the living state. The identification of any 

 substance in the deposit is a difficult matter even for the expert. 

 The vegetable and animal organic life seems to possess illimitable 

 forms, fascinating enough to study, but without profit to the average 

 observer. Those who wish to pursue the biologic features of water 

 should consult any of the well-known text-books on the subject. 

 The identification of mineral matter may in part be effected by the 

 aid of the microscope and completed by the use of chemical reagents. 

 Sand appears as large angular masses; clay as round, smooth 

 globules; chalk smooth, but of crystalline appearance. If chalk is 

 suspected, a little dilute hydrochloric acid run under the cover- 

 glass will settle the point, for, if it is chalk, it will dissolve with the 

 evolution of gas. Oxide of iron shows as a reddish-brown 

 amorphous mass which will turn blue if a drop of potassium ferro- 

 cyanide solution be run under the cover-slip. 



Dead animal matter is more easily recognised than is the case 

 with vegetable matter. Vegetable tissues should, however, always 

 be looked for and, if possible, identified so as to trace their source 

 of origin. Linen and cotton threads and portions of household 

 vegetables point to the presence of house waste. Wool, hair, 

 muscular fibres and starch granules strongly indicate contamination 

 with sewage matter. 



Bacteriological Examination. The bacteriological examination 

 of water may give some idea of its suitability for drinking purposes. 

 Like other tests it is subject to the possibility of errors, and its 

 usefulness, though of undoubted value under certain circumstances, 

 is not without limits. 



In general, the bacteriological examination of water is done 

 for the purpose of estimating the total number of bacteria in a given 

 volume, such as one cubic centimeter; to isolate and discover the 

 kinds of bacteria that are most numerous and to search for specific 

 pathogenic organisms. 



All waters, except perhaps those derived from artesian wells, 



