RURAL ENGINEERING. 301 



eventually reacted strongly, did not begin to ammonify until after periods of 10 to 

 14 days. Similar phenomena have been noted with regard to the reaction of the 



cultures on nitrate-." 



The behavior of the different cultures was very variable both as regards rate of 

 action and character and proportions of the reduction products. 



"Regarding the distribution of ammonifying and denitrifying bacteria in sewage 

 and the effluents from sewage filters, based on a Btudy of the biochemical functions 

 of over 300 representative cultures from a variety of samples, it may be said thai a 

 majority of the bacteria from these Bources, which are determinable by the ordinary 

 plate methods, using gelatin as a culture medium, reduce nitrate- and decompose 

 peptone into ammonia, although these two functions are not always present in the 

 same species. By the use of quantitative tests tor the a unt of liquefaction pro- 

 duced in gelatin by over 150 of these cultures, we have hern able to determine 

 approximately the relation between the peptonizing power, or power to liquefy 

 insoluble organic matter, and the ammonifying and denitrifying powers of 

 bacteria. 



"We find that while many nonliquefying bacteria are able to reduce nitrate- or 

 to ammonify peptone or to do both, and many liquefying bacteria do nol possess 

 these functions, nevertheless, in a large majority of cases, the possession of the first 

 function means possession of one and usually both of the last two functions, and the 

 average amount of change produced in the nitrogenous matter in solution is much 

 greater with peptonizing bacteria than with those which are unable to liquefy gela- 

 tin. Furthermore, an increase in the liquefying power appears, a- a rule, to be 

 correlated with increased ability to reduce nitrate- and to ammonify peptone." 



Contribution to the biochemistry of sewage purification; the bacteriolysis 

 of peptones and nitrates, s. DeM. Gage {Jour. Amer. Chem. Soc. t . No. i. 



pp. 827S6S). — Substantially the same article as that noted above. 



The effect of water on rock powders, A. S. Cushmam I U. S. Dept. Agr.. Bur. 

 Chem. Bui. 92, pp. //'. pis. 4)- — A discussion of this subject, based upon some 

 studies in the Division of Tests of the Bureau of Chemistry on the cementing value 

 of various rock samples when ground wet and dry and on the color reaction with 

 phenolphthalein of the wet-ground material, as well as upon the work of other 

 investigators along the same line. The conclusions reached are as follow-: 



"(1) The effect of wet grinding is to increase the binding power or cementing 

 value of rock powders, and there are indications that the addition of small amounts 

 of suitable electrolytes to the water will still further increase the action. 



"(2) When water comes in contact with most rock powders immediate reactions 

 take place, which are to a certain extent analogous to those which take place with 

 cement and powdered glass. 



"(3) These reactions are Bhown by the alkalinity indicated by phenolphthalein, 

 hut this alkalinity is to a great degree inhibited if the solid particles are filtered out. 



" (4) The microscope reveals an accumulation of amorphous material of a gummy 

 appearance largely associated with the surface- of the crystalline particle- as the 

 action of water proceeds. 



Evidence is given to show that the l>asi<- ions sel free associate themselves 

 to a certain degree with the solid particles, leading to a concentration of the acid 

 ions in the clear solution. 



" (6) It is shown that the behavior of rock powders after being acted on by water 

 is similar to that of coagulated colloids artificially prepared in the laboratory, and 

 that the formation of colloids upon the surfaces of the particle- would account for 

 the increased binding power under the action of wet grinding. The word ' pectoid ' 

 is recommended to describe the condition of the particle- as being more appropriate 

 to the connection in which it is used than the word- 'colloid" or 'hydrogel.' 



