190 REIBLING AND REYES. 
D. Concerning the tensile strength: 
(a) That the average of at least four briquettes representing 
at least two separate mixtures of the same sample shall 
be taken for each test, excluding any results which are 
manifestly faulty. 
E. Concerning retests: 
(a) Manufacturers should be impressed with the fact that these 
are minimum requirements; that ample provision already 
has been made in the specifications for lack of uniformity 
in testing as well as in real quality; and that a quality 
*% so superior should be demanded that, regardless of the 
variable factors, the ability of cement to pass all require- 
ments shall be a certainty. Therefore; 
(b) The results obtained from the original test shall be con- 
sidered as final unless it becomes evident that serious error 
in sampling or testing has resulted in totally misrepre- 
senting the quality of the cement. In other words, that 
“border-line” cements should be avoided as much as pos- 
sible. 
F. Concerning the practical significance of the above recommenda- 
tions: 
(a) Manufacturing conditions are such that we can not hope 
to secure Portland cement which contains no free lime. 
Also, it is realized that the proposed specifications are not 
perfect. However, we believe that the enforcement of the 
above recommendations will support and promote the best 
practise in grinding and burning, and, accordingly, secure 
greater uniformity and efficiency than the present specifi- 
cations. 
(6) Without the hearty, honest codperation of both manufacturer 
and user little can be accomplished. The degree of fineness 
and burning are important financial considerations to the 
manufacturer, and the consumer should buy on a basis of 
quality. 
(c) The testing of a great number of commercial Portland 
cements from many parts of the world has convinced us 
of the feasibility of these recommendations from both 
economic and practical standpoints, and the results ob- 
tained have disproved all claims to the contrary. For 
instance, a certain manufacturer in America stated that 
owing to a long sea voyage he could not guarantee his 
cement to pass the 3.10 requirement for specific gravity. 
Our work showed conclusively that cement stored in good 
barrels undergoes very little change due to atmospheric 
influences and many cements imported from Europe and 
America show consistently a gravity above 3.10 and a low 
loss by ignition. These are the cements which, as stated 
in the Introduction of our work, show the most remarkable 
uniformity in physical properties. 
(2) We desire to emphasize the importance of the calcium hy- 
droxidephenol microscopic test for free lime, as in every instance 
a 
