162 ANNUAL REPORT 
This formula is thus seen to be deduced from a basic meta-silicate 
which hydrates by the taking up of a molecule of water. 
O-Ca O:CaOH 
7 SO WA a 
ace ALS 6.ca7 ed. A\A0-Ca0H 
N 
yo We 
SRO iver ONC aa 
IN 7° 
OAL 6 Gq”? OAL ean 
Fig. 14. Zulkowski’s formula Fig. 15. The same after hydration. 
for hydrolite. before hydration. 
Chatelier arrives at different conclusions by assuming that the granu- 
lated slags combined with lime are rendered chemically active by retain- 
ing the latent heat otherwise given off in crystallization. Prost has in- 
vestigated this point and has really found that crystalline (slowly cooled) 
slag on dissolving in hydrochloric acid evolved 301 calories, while the 
granulated slag gave off 420 calories. 
Selection and Granulation of Slags.—The limits of composition 
have already been given by the values established by Tetmayer, and it 
might be said that the more basic the slag, the better suited it is for cement 
making. The slags especially suitable for this purpose show from 27 
tONZ2ipet Cents silica, TO to) 22)per centealuminayAS tO50) peticentasmiiie, 
I to 2 per cent. magnesia. The sulphur content should be carefully 
watched and never allowed to run above 1.25 per cent. 
It is of the greatest importance to reject any slag not suitable for 
cement making and to make use of it in connection with the manufacture 
of slag brick, for which purpose the slag may be of inferior quality, that 
is, much less basic. In this manner it is possible to maintain a higher 
grade of excellence without financial loss. It is advisable therefore to 
have a slag brick outfit in connection with a slag cement plant. The 
fitness of a slag is determined by chemical analysis, which must be sup- 
plemented by physical tests; the dried granulated slag must be ground 
together with varying proportions of dry slaked lime, usually from 5 to 
15 per cent., and tested for tensile strength and constancy of volume as 
prescribed by the standard cement specifications. 
The granulation may be carried out in two ways: by means of a- 
stream of water or by means of a blast of air. There is no question 
but that the first method is the more satisfactory one, resulting in the 
best quality of granulated slag, but it has the disadvantage of producing 
a wet slag which must be dried. The amount of water retained by 
the slag is not great, however, and hence the extra cost of manufacture 
is not an important factor. Some theoretical advantages, on the other 
hand, are claimed for the air cooled slag, but these are not proved suf-. 
ficiently by actual results. The slag is granulated by means of a flat 
