368 CEMENT MATERIALS AND INDUSTRY. [bull, 24J 
which is charged, locked, operated for a sufficient time to pulverize 
both constituents of the mixture, and discharged. The disadvantage 
of this intermittent system are obvious and it seems especially unfitte 
for American conditions. The statement that no continuously operate 
mill was able to handle the mixture seemed improbable in view of th 
great variety of material successfully handled by the modern bal 
and tube mills when operated continuously in Portland-cement prac- 
tice. Several years ago the writer referred the question to a lead 
ing firm of manufacturers, and was informed that nothing in thei 
experience justified the unfavorable conclusion; and that their contiq 
uously operated tube mills had successfully pulverized mixtures J 
slag and lime. It seems probable that the most economical practice 
followed at several of the American plants, would be to send the drie 
slag through a Griffin mill or ball mill, mix the crushed slag wit 
lime, and complete the mixture and reduction in continuously oper 
ated tube mills. Whatever system of reduction is employed it m 
necessary that the slag be dried as completely as possible, and withli 
modern driers the amount of moisture in the dried slag can be eco- 
nomically kept well below 1 per cent. 
Slag cements normally set very slowly, relative to Portlands. As> 
this interferes with their use for certain purposes, many attempts haver 
been made, by various treatments, to reduce their setting time. Tlieret 
is, unfortunately, another reason wiry the manufacturer should desire 
to hasten the set of his product. Most of the slag cements sold in this* 
country masquerade as Portland, and it is desirable to the manufac- 
turer therefore to make such of their properties as are brought out in J 
ordinary tests or analyses approximate to those of true Portland 
cement. The set of slag cements can be hastened by the addition of ij 
puzzolanic materials. Of these burned clay, certain active forms of fl 
silica, and slags high in alumina are the cheapest and most generally 
obtainable. The most important method of regulation is, in this coun- j 
try at least, the Whiting process, which is followed at two large 
American plants. 
United States Patent No. 544706, issued in 1895 to Jasper Whiting, 
covers the use of "caustic soda, potash, sodium chloride or equiv^ 
alcnts, or any substance of which the latter are ingredients,' 1 added 
either as aqueous solutions or in a dry state at any stage of the process 
of slag-cement manufacture. In the specifications accompanying th( 
application for this patent, the patentee states that in the case of dry 
caustic soda the amount added will vary from 0.125 to 3 per centt 
"depending chiefly upon the use for which the cement is intended.' 
The patent was subsequently conveyed to the Illinois Steel Compaivy. 
and the process covered by it is used by that company in the manufac- 
ture of its " Steel Portland " cement. A license has been issued to th( 
