166 CONTRIUUTIONS TO OUR KNOWLEDGE OF SOIL-FERTILITY, xvi., 



could combine with the earthy hydrates. Heating the mould 

 increased the amount of acid, and the increase was largely soluble 

 in water. 



Humus with Calcium Carbonate. 



According to the earlier lime-water test, in which 100 grams 

 of dry organic matter absorbed 383 c.c. of N/1 alkali from lime- 

 water, it appeared that a neutralisation of the acids of the leaf- 

 mould would be obtained by adding 2 grams of calcium carbonate 

 to each portion containing 10 grams of dry organic matter, and 

 that neutralisation would be certain if 2*5 grams were added. 

 A set of bottles were prepared, each receiving the equivalent of 

 10 grams of dry organic matter, and 2*5 grams of calcium car- 

 bonate as precipitated chalk. The bottles were sterilised for 

 two hours at 130", then moistened and stirred with 15 c.c. of 

 water, and steamed for an hour. Subsequent tests showed that 

 sterilisation had been complete, and that the extracts furnished 

 by the tests were neutral to phenolphthalein. Sets were infected 

 with certain micro-organisms and incubated at laboratory tem- 

 peratures for varying times. It will be remembered that the 

 organisms T.P.2 and Actino. 14 were chosen because they in- 

 hibited the growth of spreading bacteria and moulds on agar- 

 plates. A test made at the beginning of this experiment showed 

 that T.P.2 had lost its toxic power, while Actino. 14 had not. 

 In view of this, the bottles of T.P.2, which had been infected, 

 were incubated in an atmosphere of carbon dioxide, to see if 

 this would have any influence in restoring the toxicity. Several 

 of the portions, which were tested on the eighteenth day, were 

 unfortunately destroyed. 



