44. ANNUAL REPORT 
Blast furnace slags are bodies closely akin to glasses and might be 
considered alloys in character. It is, of course, evident that the com- 
position of the slag is dependent on the compositon of the ore as well as on 
the kind of pig iron it is desired to produce. Ii the ores used are uniform 
in character, the slag. produced will also be regular in composition as lone 
as the same grade of iron is being made. It is obvious that an ore 
high in silica will require more limestone for fusion than one lower in this 
constituent ; an increase in the sulphur or phosphorus in the ore will also: 
necessitate an increase in the lime content of the slag. The foundry- 
man in trying to smelt iron cheaply and yet maintain a good quality is 
certain to make a slag of a variable composition. Since the slag is the 
by-product, it is of importance only so far as its composition and fluidity 
affect the working of the furnace and the quality of the iron. Some limi- 
tations are met, however, in the fluctuation of the slag, as it will not melt 
and flow freely, if its composition departs too far from the usual range.. 
Thus it is often impossible to remove all the impurities, sulphur and phos- 
phorus from the iron, as the high content of calcium necessary would make 
the resulting slag too refractory. If the slag is to be used for the manu- 
facture of slag cement, proper allowance must be made for the fluctuations. 
in the composition resulting from the variations in the composition of the 
ore. Slag of improper composition should be rejected for the making of 
pozzuolane cement, though it may be used for the manufacture of slag 
brick. The rules of Prof. Tetmayer, given above, which he has deduced: 
from a great number of analyses and experiments, will serve as a guide for 
the selection of a slag. | 
In the tables on pages 45 and 46 are given the ana'yses of a number 
of European blast furnace slags which were made the subject of an inves- 
tigation pertaining to slag cements by Prof. L. Tetmayer,* excepting 
ING, Alte | 
Prof. Tetmayer also made an elaborate series of tests with these 
slags in the granulated condition by grinding them together with various. 
amounts of hydrated lime and testing them for tensile and crushing 
strengths. These resu‘ts, representing mixtures with 15 per. cent. of lime,. 
are plotted in the accompanying curve, figure No. 2. 
These results seem to show that the general tendency of the slags 
is to correspond to the Tetmayer ratio, although this fact is brought out by 
no means sharply. We must remember, however, that other factors 
enter into the resulting strength of slag cements, such as the degree of 
liquidity, the degree of granulation of the slag, ete. Until additional 
experimental data are collected the results of Tetmayer must, as a whole, 
be accepted. Prost and Mahon take exception to his limits with reference 
to the alumina, as they have obtained good results with higher alumina 
contents. 
*0, Tetmeyer; Resultate Specieller Untersuchungen Hydraulischer Bindemittel, Zuerich 
1897. , 
