278 WATER HYGIENE 
TURBIDITY 
By turbidity is meant the suspended matter which is usually present 
in water from surface sources. This is gathered from the water shed 
and, as long as sufficient velocity is maintained, is carried along. Few 
people care for a turbid water although they may become educaied to 
the appearance and use of a water having much matter in suspension. 
There seems to be little sanitary significance connected with the tur- 
bidity. This, of course, depends upon the kind of matter which makes 
up the turbidity. 
Determination. Several methdds are available for the determina- 
tion of turbidity. A convenient method is the comparison of the sample 
of water to a “silica standard.” This “ silica standard” is a 0.1 per 
cent suspension of diatomaceous earth in a liter of distilled water. This 
suspension has a turbidity of 1000 or contains 1000 parts per million of 
silica. This solution may be diluted with distilled water to give stand- 
ards of 5, 10, 15, 20, 30, 40, 50, ete. These standard solutions should 
be stored in clear glass bottles, preferably of the same type in which the 
samples are taken and should be thoroughly shaken before using. The 
sample and the standard should be compared by viewing any dark object 
and noting the details of each. 
CoLor 
Color is of little sanitary significance. It usually comes from 
organic matter and often is removed from water with difficulty. Very 
often other substances such as iron may color a water. 
Determination. The platinum-cobalt method for determining color 
is the standard. The standard solution is made by dissolving 1.246 
gms. of potassium platinic chloride (PtCl,-2KCl) containing 0.5 gm. 
platinum and 1.00 gm. crystallized cobalt chloride (CaClo-6H.20) 
containing 0.25 gm. cobalt, with 100 ¢.c. of concentrated hydrochloric 
acid in distilled water and diluting it to a liter. Such a solution is the 
standard having a color of 500. It should be diluted to give standards 
of from 5 to 80. These may be kept in 50 c.c. Nessler tubes which should 
be carefully protected when not in use. 
The sample of water should be shaken and 50 c.c. poured into a 
clean 50 c.c. Nessler tube. Compare this with the standards in a color- 
imeter. Standard methods prescribes the recording of results as follows: 
Color between land 50 recorded to nearest unit. 
Color between 51 and 100 recorded to nearest, 5. 
Color between 101 and 250 recorded to nearest 10. 
Color between 251 and 500 recorded to nearest 20. 
