to produce commercially. In fact, the ground clinker sets 
too fast for commercial use. To retard this, a small pro- 
portion of gypsum is added. 
The principal advantages of portland cement over other 
cements are in the uniformity of the product, in the strong 
binding qualities and in the nicety to which the setting 
time can be regulated. 
Although the making of cement provides employment 
for many men, a large part of the work is done automatically. 
A visit to the Universal plant shows buildings that seem 
tenanted only by great machines going steadily about their 
tasks of drying, crushing, burning and powdering materials 
into cement every hour of every day the year around. 
A trip to a Universal plant not only impresses the visitor 
with the large scale of manufacturing operations, but with 
the facilities for handling, sorting, cleaning and repairing 
sacks. The company has more than 25 million cloth sacks 
that are either at its plants or in the hands of customers. 
The charge for sacks, as all cement buyers know, is invoiced 
with the cement, but a full refund is given for every sack 
that is returned in good or repairable condition. If this 
charge were not refunded, it would have to enter into the 
cost of building. During the war, sacks cost as much as 
35 cents and were invoiced with the cement at 25 cents 
each. At the present price of 10 cents a sack, the charge for 
sacks on a job requiring 20,000 sacks of cement would total 
$2,000. The builder gets a large part of this $2,000 back— 
he gets 10 cents back for every sack that is returned in good 
or repairable condition. That this right to return cloth 
sacks and obtain refunds therefor is a privilege that saves 
millions of dollars to the building public annually is better 
appreciated when it is recollected that there are nearly 
100 million sacks of cement used in the United States each 
vear. 
The sacking of cement is an interesting process. The 
bags themselves are out of the ordinary in that the tops 
are tightly wired before being filled and that the filling is 
done through a self-closing vent in the bottom. This vent 
is slipped over a spout or nozzle, a lever is pulled, cement 
Hows into the sack and it quickly swells much as a toy