STATE GEOLOGIST. Irak 
only the question of cost. It would hardly pay to purchase Portland 
cement on the market for this purpose and it would hence be necessary 
to produce it at the works, which could be done without any practical 
difficulty by using slag and limestone. But, on the other hand, the ques- 
tion arises: Why not make Portland cement altogether from the slag 
available, and thus eliminate the peculiarities of slag cement which re- 
quires constant moistness and careful drying though; sacrificing the 
increase in tensile strength obtainable by the use of slag? This question 
cannot as yet be answered definitely, as we do not know the properties 
of the Portland-slag cement very thoroughly. If this cement can fill 
the requirements put to Portland cement, there is no reason why it 
should not compete with the latter. If it cannot, its manufacture must 
be governed by the market conditions and it should be sold only for 
purposes for which it is entirely suitable, viz., underground or subaqueous 
work. ‘The present indications are that the “Iron Portland” cement is 
suitable for much work in which the standard Portland cement is 
employed, but this cannot be accepted as being established. Until proven 
otherwise, all slag cements and mixtures must be considered inferior to 
Portland cement with regard to all around usefulness. But recent 
European evidence brings out much in favor of the Iron Portland 
cement. 
Summarizing, we have these two kinds of processes which utilize 
slag: 
First, manufacturing slag cement, using slaked lime, and converting 
all unsuitable slag into slag bricks. 
Second, manufacturing Iron Portland cement, using the inferior 
grades of slag for producing the Portland cement necessary in this 
process, since in this way it can be corrected, if defective in composition, 
by the addition of limestone. Either process provides for any unsuitable 
slag and hence eliminates waste. The diagrams on pages 172 and 174 
indicate in a general way the arrangement of these two types of plants. 
Slag Brick.—These, made from a mixture of granulated slag, slaked 
lime and crushed, hard slag in various proportions, from 75 parts of 
granulated slag, 8 per cent. of slaked lime and 17 of hard slag down 
to 30 parts of granulated slag, 3 parts of slaked lime and 67 parts of hard 
slag, are being made in large quantities and have proven entirely stitable 
as far as strength is concerned, as they show crushing strengths far 
beyond the requirements. Their chief drawback is in the undesirable 
gray color and the tendency to “whitewash” owing to the presence of the 
sulphur salts. The manufacture is extremely simple, consisting of grind- 
ing both the granulated and hard slag to a fineness between about ten and 
twenty mesh sieve, mixing the two kinds of slag with the slaked lime in a 
mixer of the pug mill type, moistening the mixture till damp and 
