130 ANNUAL REPORT 
that it is present quantitatively, but also whether it is qualitatively suitable 
as well. It shows whether the silicate matter which is present, is in a 
form in which it will be readily assimilated into the calcium silicates to be 
formed, or whether it is in such physically unfit condition that only a lim- 
ited part of it will be useful. 
In the latter case, using the data furnished by the older methods, the 
cement-maker is likely to produce a cement too poor in combined silica. 
Or, if he recognizes this danger, and uses an excess of clay to bring the 
proportion of available silica up to the proper point, he runs into the 
counter difficulty of bringing in too much alumina. 
This method of analysis enables us, therefore, to discriminate between 
clays as to their cement making value. An ideal clay when heated with 
calcium carbonate and treated with hydrochloric acid and sodium car- 
bonate solution should show practically no insoluble residue, and as a 
rough approximation it might be said that no clay considered for cement 
making purposes should contain more than Io per cent. insoluble residue. 
If, hence, a clay has the proper alumina-silica ratio and shows a small 
insoluble residue without extremely fine grinding it may be said to be 
entirely suitable for cement manufacture. Likewise, this method fur- 
nishes a most excellent guide as to the fine grinding of the raw materials, 
‘that is, how long a given mixture must be ground in order to show com- 
plete solution which is equivalent to perfect chemical activity. On the 
other hand it shows also when we are grinding a mixture too long, that 
is, when we are expending unnecessary power on this operation. 
The heating of the clay-calcium carbonate mixture may be done over 
any good blast lamp. 
ANALYSIS OF CALCAREOUS MATERIALS. 
In this connection we must clearly distinguish between the accurate 
academic methods of analysis and the rapid methods practiced by the 
factory chemist which lack more or less in accuracy. Owing to the 
various modifications of methods employed in cement practice the results 
obtained by the various chemists must show considerable variation. The 
Society of Chemical Industry has endeavored to systematize analytical 
methods pertaining to the analysis of calcareous materials and its com- 
mittee has proposed the following tentative method,* as suggested by 
Mr. Clifford Richardson and modified by Mr. W. F. Hillebrand for the 
analysis of limestones, raw cement mixtures and Portland cement: 
EXACT METHODS. 
Solution.—One-half gram of finely powdered substance is weighed 
out and, if a limestone or underburnt mixture, strongly ignited in a plati- 
num crucible over the blast lamp for 15 minutes. It is then transferred 
*Report of the Subcommittee on Uniformity in Analysis of Materials for the Portland Cement 
Industry. Jour. Society Chemical Industry, No. 1, 1302. 
