212 EXPEEIMENT STATION RECORD. 



date the rainfall was 26.77 in., falling on 1S2 days, and containing the e(iniva- 

 lent of 20.22 lbs. of common salt per acre. 



Composition of Indian rain and dew, J. W. Leather {Mem. Dept. Afft: India. 

 Cliciii. So:, 1 iWOG), \o. 1. pp. 11; ahs. in Jour. Chcm. Soc. [London], 90 

 (1906), A^o. 525, II, p. .}<S'7'). — "Determinations of nitrogen as ammonia and as 

 nitrates and nitrites in samples of rain water (generally two per month) col- 

 lected at Dehra Dun from January to December, 1904, and at Cawnpore from 

 May 1, 1904, to April 30, 1905. 



"The dew collected in a large gage (loVo ^^c-re) at Cawnpore from September 

 16, 1904, to March in. 190."). amounted to 0.170 in. and contained nitrogen ammo- 

 nia =0.0.'").") and nitric nitrogen=0.(i.j6 lb. per acre, the amounts per million vary- 

 ing from O.s.l to 2.(;."'> and o..")! to 4.12, respectively." 



The prevention of the grovsrth of algae in water supplies (Engin. Rcc, 5.'i 

 (1906), lS!o. 10, pp. 26S, 26^). — An abstract is given of a paper presented at the 

 last annual meeting of the Royal Sanitary Institute by S. Rideal and R. 

 Orchard, reporting results of comparative tests of Moore's copper sulphate 

 method and treatment with electrolytic chlorin. The use of 1.2 parts of the 

 latter per million parts of water was more effective than 1 part of copper sul- 

 phate per million. The chlorin treatment is considered an effective means of 

 preventing green growths in water and of destroying a large proportion of 

 microscoiiic jtlnnts which are found in water. 



A study of the numbers of bacteria developing at different temperatures 

 and of the ratios between such numbers with reference to their significance 

 in the interpretation of water analysis, S. De ]\I. Gage (Boston. 1906, pp. 

 223-251). — This is a reprint from Biological Studies by the Pupils of William 

 Thompson Sedgwick. 



In the investigations reported in this paper 17 different classes of samples of 

 water were examined. These classes and the methods used in their investiga- 

 tion are described. 



The results obtained lead to the conclusion that "nearly all of the informa- 

 tion desired concerning the bacterial content of water may be obtained by the 

 use of selective media, by the use of selective temperatures, or by a proper 

 combination of the two. In the present investigation the selective action of 

 four different temperatures, 20°. 30°, 40°, and i")0° C, and two different media, 

 regular agar, and litmus-lactose agar, in determining the bacteriological con- 

 tents of a numlier of different kinds of water, have been studied ; and while the 

 results obtained have been in many cases inconclusive, and in other cases too few 

 in number to warrant the drawing of any far-reaching conclusions, they indicate 

 in a measure the procedures which must be followed in order to place the bac- 

 teriological analysis of water on the same plane as the chemical analysis." 



The substitution of litmus-lactose agar for agar or gelatin as culture 

 medium is recommended on the ground that the former permits the simultaneous 

 determination of the total bacteria and of the acid-producing organisms with- 

 out appreciably increasing the labor involved. " The numbers of the two classes 

 of bacteria so determined indicate more completely the character of the water 

 than would the numbers of either class determined alone." 



The total numl)er of bacteria determined at 20° C. is not of special significance, 

 but the number of acid-producing organisms at this temperature is an important 

 check upon the total numbers. The number of bacteria and of acid-producing 

 organisms determined at 30° C. after 24 hours' incubation affords a means of 

 more sharply distinguishing between polluted and pure waters than the num- 

 bers determined at lower temperatures. " The numbers of bacteria determined 

 at 40° C. are of great interest, since in this class of bacteria must be included 

 the disease-producing organisms. The distinction between waters of different 



