STATE GEOLOGIST. 155 
in order to correspond to actual conditions. This agrees very well with 
the results obtained for all velocities between 0.1 mm. and 12 mm. per 
second, which corresponds to the ordinary clay and silt elutriation. 
The apparatus which is used to carry out this method of separation 
has probably first been used on an extensive scale by Noebel. But con- 
siderable improvements have later been made by Dietrich, Masure, Schoene 
and Mayer. A good method of working and a very satisfactory apparatus 
have been worked out by Mayer, who improved the Schoene silt apparatus. 
But all of these methods, though extremely useful for exact separa- 
tions, are too elaborate to be used in daily routine of a cement works 
iaboratory, and hence cannot be discussed here in detail. There can be 
no doubt that the method of moving liquid is more accurate than the 
subsidence method. [or most rigid scientific accuracy the Hilgard method 
using a perfectly cylindrical funnel and a mechanical stirrer is considered 
the best. Yet the fact remains that for all around simplicity and rapidity 
of working the subsidence method must remain the one most satisfactory. 
SPECIAL ANALYTICAL AND PHYSICAL PROBLEMS CONNECTED WITH CEMENT 
ANALYSIS. 
Among the problems of indirect importance to the practical cement 
inanufacturer, but of theoretical interest to the chemist, are such problems 
as the amount of free lime in cement, the amount of chemically combined 
water in hardened cement, the amount of ferrous and ferric iron present, 
the condition of the sulphur in the clinker, whether sulphide or sulphate, 
the degree of absorption of sulphur from the fire gases, the alkalinity of 
different cements, the melting points of cement and cement mixtures, the 
effect of the composition and rapidity of cooling upon the crystallization, 
the heats of solution and hydration and many other problems. 
Briefly considering these various problems, we find that the question 
most profoundly interesting cement technologists has been the query as 
to the amount of free lime present in cement. This problem has been 
attacked from all sides, and with practically no results. Thus Liamin, a 
Kussian investigator, endeavored to determine the amount of free lime 
by calculations from the amount of water given off at different tempera- 
tures. Tomei based his work on the action of ammonium chloride on 
Portland cement, while Hauenschild used other solutions of ammonium 
salts. Rebuffat made use of a sugar solution, while Zulkowski used a 
very dilute acid solution. Steuer allowed hydrogen sulphide to act upon 
water in which Portland cement had been poured; Wormser and Spanjer. 
made use of an alcoholic solution of aluminium chloride for leaching out 
the calcium oxide, while Hart employed a 10 per cent. alcoholic iodine 
solution. Wagner studied the action of carbon dioxide upon cement 
heated to a red heat, and finally Passow made use of the fact that heat is 
evolved when calcium oxide combines with carbon dioxide at a red heat. 
H. W. Wiley, Agricultural Analysis, p. 2138. 
