Aprenry—Dissolved Gases and Fermentative Changes. 275 
to differ in fermentative properties, which, however, I do not anticipate. The 
ratio of organic carbon to nitrogen of the total organic matters in the fermented 
sludge was 7 : 1.* 
The experiments with the organic matters above described were carried out in 
accordance with the methods described in my first Paper. The analytical deter- 
minations, made before and after keeping the various solutions, employed for 
experiment, out of contact with air, are recorded in the following Table XVIII. 
The first solution (#) was prepared by dissolving a known weight of the humus 
in distilled water and a little sodium carbonate; and when the solution was 
complete, a few drops of sediment from one of my old experiments with peat 
extract were added for the purpose of seeding, together with the necessary mineral 
salts, and the whole was diluted to the necessary bulk with distilled water. 
The solution H’ contained a similar quantity of humus in solution as 7, but 
more sodium carbonate, and, in addition, ammonium chloride. 
* Tt should also be noted that an examination of wet portions of the fermented sludge was made at the 
time the above analysis was carried out, with the view of ascertaining whether there still remained in the 
sludge any organic matters which had not undergone complete carbon-oxidation. For this purpose, about 
40 grms. of the sludge were saturated with 2 litres of water; and portions of the water, with the sludge 
matters in suspension, were transferred to bottles and preserved out of contact with the air for 21 days, 
according to the method I have described. On examination of samples (in which, of course, the matters 
in suspension had previously been allowed to completely subside), before and after keeping, indications of 
a considerable fermentative change were found. The whole of the dissolved oxygen had been consumed 
during the period of keeping out contact with air, and a large volume of carbon dioxide formed ; but inas- 
much as no appreciable increase in the amount of ammonia, originally present, was detected, and the water 
remained perfectly free from unpleasant odour, or any other indication of putrefactive fermentation. It 
appeared evident that the fermented sludge, at the time I commenced my examination of it, contained only 
small quantities of organic matters that had not undergone complete carbon-oxidation. No nitrous nor 
nitric acid was detected in these solutions, either before or after keeping. 
