182 REIBLING AND REYES. 
(8) The following changes which account for all the variations 
met with in the action of a commercial Portland cement may oc- 
cur in the rate of set and in the plasticity, namely: 
1. An acceleration of the set and an increase in plasticity as regauging 
is eliminated with the first slaking of free lime. 
2. A retardation of the set,and a further increase in plasticity with 
the further slaking of free lime. 
8. An acceleration of the set and a decrease in plasticity as the 
slaked lime is diminished by conversion into calcium carbonate. 
4. A retardation of the set and a further decrease in plasticity as the 
cement tends to become inert after prolonged exposure. 
(9) The practical control of the setting properties: 
(a) An analysis, such as is outlined, of the cement before it is packed 
is an accurate means of ascertaining the possible effects of 
storage on the setting properties. It will inform the manu- 
facturer if the set of the product of his kiln is capable of 
being kept within desirable limits during storage, and will 
indicate the amount of retarder required. 
(6) Sometimes a cement must be seasoned before its set can be con- 
trolled; but in most instances this is not necessary, and in all 
instances the necessity for seasoning can be avoided by proper 
burning. 
(c) The manufacturer must give special consideration to the effects 
of hydration of the free lime and not to its conversions into 
carbonate. 
(d) Proper packing is necessary for best results. 
(e) Almost all commercial cements, which failed to pass standard 
specifications on account of their rate of set, would have 
proved satisfactory had they been seasoned or plastered 
properly. 
(10) A study of the influence of fineness upon the rate of set 
shows that it requires only the use of a small additional quantity 
of retarder to overcome this influence, and, with few exceptions, 
it is certain that manufacturers can control the set of their 
product even though it is all ground to an impalpable powder. 
(11) Special attention is directed to the following results: 
(a) Manufacturers especially should give the subject of partial regaug- 
ing due consideration, in order to avoid shipping cements which, 
although apparently slow setting at the mill, are apt to be 
quick setting when tested at their destination. 
(b) The policy of using a minimum amount of gypsum has often 
resulted in quick setting material where 0.5 per cent of addi- 
tional retarder would have prevented all trouble. 
(c) Exception is taken to the deductions of Conover that quick cooling 
of the clinker slows the set of the finished product. 
