40 KANSAS ACADEMY OF SCIENCE. 
sibility that the carbon dioxide should escape, and the comparison of the first 
and last samples show that this is the case. The carbon dioxide in the first was 
3.52 and in the last 3.55 per cent. 
There is a wide variation in the per cent. of calcium and magnesium carbon- 
ates in different samples, and the positive effect of different quantities of this 
substance has not been ascertained. From what is known, the magnesium plays 
very little part in the determination of the quality of the set cement. The amount 
of water in the manufactured plaster seldom falls much below five per cent. ; the 
variation being not over two per cent. when a number of analyses are compared. 
Something should perhaps be said about the use of ‘‘retarders”’ in cement 
manufacture. They are especially used with the rock plasters, though occasion- 
ally, no doubt, with the cement plasters. The common opinion is that sours and 
sweets act as retarders, and many substances of these classes are used, such as 
citric acid and sorghum molasses. It is possible by the judicious use of sucha 
retarder to delay the setting of the cement many hours, when it would normally 
set ina few minutes. The action of these materials seems to be to prevent the 
material hardening by the formation of the crystalline compound. On the other 
hand, there are some things that act as accelerators, and in mixing the plasters 
they must be rigidly excluded. For instance, if a plaster is mixed in a vessel 
which contained some plaster that has previously set, the setting is very much 
accelerated. This would very readily remind one of the production of sudden 
crystallization in saturated solutions by bringing into them crystals of the same 
material. A number of other problems in connection with the specific gravity of 
the material, the amount of water that should be left in the manufactured prod- 
uct, and similar topics, remain to be investigated. 
ON THE OCCURRENCE OF NITRATES IN WELL-WATERS. 
BY E. H. S. BAILEY, LAWRENCE. 
Read before the Academy December 30, 1898. 
It is a well-known fact that the ammonia of the air, as well as the small 
quantity of nitrates and nitrites therein contained, is washed into the soil by the 
rains, and this water there comes in contact with the organic matter of the soil, 
and oxidation takes place. This organic matter is first converted by the proc- 
esses of decay into ammonia, and this in turn changes to nitrites and finally to 
nitrates, in which latter form it is available to aid in sustaining plant life. 
The process of ‘‘ nitrification,’’ as it is called, may go on in surface-waters, as 
in ponds and streams, and is carried on very extensively in the upper layers of a 
loose, porous soil, where the oxygen of the air has an opportunity to assist. 
This whole matter has been very extensively studied, within the past ten 
years, in its applications to agriculture, and also in its applications to the impu- 
rities of water and the purification of sewage. The admirable reports of the 
Massachusetts Board of Health, especially for 1890, on the purification of water 
and sewage, show the very extensive experiments which have been carried out, 
and the results of these researches, which have become almost classic. There 
has been a growing belief in the importance of ‘“‘bacteria’’ in producing the 
change formerly ascribed to simple chemical oxidation. Although great diffi- 
culty has been experienced in isolating and cultivating the specific bacteria that 
are necessary to produce the change, yet the latest researches show that this can 
be done, and that water that has been sterilized can be treated with ammonia 
