108 BACTERIA AND THE DISINTEGRATION OF CEMENT, 



carbonic acid and the decomposition of the cement seemed 

 unaccountable. When the reservoir was faced with a cement 

 containing a percentage of siHca higher than the original cement, 

 •no further disintegration was observed. 



A disintegration of the cement canals used in conveying the 

 Sj'dney water supply has been observed for some time by the 

 engineers. Acting under instructions from the Council of this 

 Society, and upon the invitation of Mr. Darley, Engineer-in-Chief 

 for Public Works, I visited the faulty canals on September 8th, 

 1900, under the guidance of Mr. Small, Engineer to the Metro- 

 politan Water Supply Board, and collected samples for laboratory 

 examination. 



The cement above the water line was absolutely hard, while 

 below the water it was soft, and the surface could be easil}'' 

 scraped off with a blunt nickel spatula to a depth varying from 

 Y^g to J inch. To get samples deeper into the cement a pick was 

 used. The material easily broke away. The samples included 

 the blackish sediment at the bottom of the canal, a scraping 

 from the surface of the side, and the sand}' debris at depths of 

 one, four and six inches. 



So far as the history of the cement is concerned, the canal was 

 made some 18 years ago, when, I am informed, cement was 

 bought by the brand, whereas now all cements are tested physi- 

 cally by the Board before purchase. This should be borne in 

 mind, because the disintegration may be purely and primarily 

 chemical and not at all the result of chemical action induced by 

 living micro-organisms. 



In endeavouring to obtain organisms which might cause the 

 disintegration, it would obviously be useless to separate all the 

 bacteria that are present in the samples. Since the cement is 

 impregnated with water, all the organisms that are in the water 

 would be found. We ought rather to try to exclude Ijacteria 

 which would not be expected to have an action upon the cement. 

 This means the employment of methods of culture or media as 

 permit the growth only of such organisms. ' To fix upon these 



