382 THE NITRIFYING BACTERIA. 



hydrated in the walls ; calcium carbonate and a little alkali are 

 present in the brickwork, and there is no lack of the necessary 

 oxygen. Consequently all the preliminary conditions favouring 

 the activity of the nitrifying bacteria introduced in dust, &c., 

 are fulfilled. However welcome this activity may be when re- 

 stricted to the soil, it is entirely undesirable in brickwork, the 

 latter being gradually corroded and rendered brittle by the calcium 

 nitrate produced. Sprinkling the walls with powerful antiseptics, 

 such as antinonnin, may, however, afford a remedy. That the 

 phenomenon is really due to the nitrifying bacteria has been proved 

 by the researches of 0. HELM (II.) and G. TOLOMEI (II.). 



A few words must also be devoted to the saltpetre plantations. 

 Since the discovery of the South American deposits of nitrate of 

 soda, which substance can be converted into saltpetre by treatment 

 with potassium salts, the production of plantation-saltpetre has 

 decreased. It will, however, come to the front again whenever 

 the Chilian beds are exhausted. In fact, the production of salt- 

 petre for agricultural purposes by this method is even now worthy 

 of consideration. The quantity of Chili saltpetre imported by 

 European countries is very considerable, and large sums of money 

 are annually disbursed to South America which might be retained 

 by producing the saltpetre at home. The accomplishment of this 

 project necessitates a searching investigation of all the conditions 

 of nitrification, in order to ascertain how the reaction may be 

 suitably controlled. The result would be that, instead of using 

 expensive foreign nitrate, the ground would be manured with cheap 

 sulphate of ammonia, now formed as a waste product in home gas- 

 works and coke-factories, and put upon the market in constantly 

 increasing quantities. The consequent freedom from the hands of 

 Chilian speculators would be a great gain from the point of view 

 of national economy. Moreover, this method of manuring presents 

 another advantage from the standpoint of the agricultural econo- 

 mist. As is well known, the soil has no power of fixing nitrates, 

 a certain portion of the added saltpetre invariably as P. DEHERAIN 

 (III. and IY.) and others have shown escaping in the drainage- 

 water, so that more has to be added to the soil than is recovered 

 in the crop. This disadvantage does not attach to manuring with 

 salts of ammonia, since they are fixed by the soil and protected 

 from wasteful lixiviation, the nitrifying bacteria then oxidising the 

 ammonia and supplying the plant with nitrates according to its 

 requirements. 



So far as plantation-saltpetre is concerned, the external con- 

 ditions favouring the rapid formation of this compound have been 

 gradually ascertained by means of tentative experiments. A pyra- 

 midal heap, resting on an impervious clay foundation, is prepared 

 by mixing chalky soil with various kinds of organic matter, and 

 is frequently watered with liquid manure, an admixture of brush- 

 wood in the heap imparting porosity and facilitating aeration. The 



