110 BACTERIA AND THE DISINTEGRATION OP CEMENT, 



The fluid on the surfaces of the cement particles cannot contain 

 much nitrogenous nutriment, and consequently those bacteria 

 which can grow and therefore be isolated in media which contain 

 minute quantities of nitrogenous material are more likely to be 

 the cause of the cement disintegration (if it be bacterial) than 

 organisms which cannot grow under such circumstances. 



There are accordingly three lines of research indicated, and of 

 these I shall begin with the nitrification. Several 100 c.c. 

 bottles were half filled with ammonium sulphate nutrient solution,* 

 plugged with cotton wool and sterilised. Portions of the samples 

 of the disintegrated cement were introduced and the bottles incu- 

 bated at 22° C. No nitrification had set in when they were tested 

 after 1 , 5, 1 3, and 39 days respectivel3^ On the 6oth day, when they 

 were again tested, nitrites were found in quantity in two bottles, 

 one of which had been infected with material taken from the 

 surface of a cemented crack at the bottom of the canal, and the 

 other with mud also taken from the bottom of the canal. On 

 the 81st and on the 101st day the bottles were again tested, and 

 the same fact observed. Two fresh bottles of ammonium sul- 

 phate were inoculated with a small loop of the nitrifying solutions, 

 and nitrites were found in these on the fourth day. 



It is seen that nitrification was obtained in the solutions of 

 ammonium sulphate that were infected with the surface layer of 

 the cement and with the mud at the bottom of the canal. It 

 was not obtained in the cement at the depths of one, four, and 

 six inches. This is important, because disintegration was in pro- 

 gress at these depths in the cement wall, and if the nitrifying 

 organisms contribute at all to the decomposition of the cement, 

 they should have been found at these places, and not only on the 

 surface where the material had become thoroughly disintegrated. 

 Stutzer and Hartleb found the nitrifying organisms in the mud 

 at the bottom of a cement reservoir. This is exactly what has 



* Ammonium sulphate 2 grms., sodium carbonate 1 grm. , potassium 

 dihydrogen phosphate 0*1 grm., tap water 1000 c.c. as recommended by 



Stutzer. 



