140 



REIBLING AND SALINGER. 



startling inconsistencies. To be more explicit, we will give, for example, 

 the following tests made under the Army Specifications for 1902: 



Two operators of considerable experience were ordered to test according to 

 these specifications a shipment of 1,000 barrels of cement under dispute. Fifty 

 samijles, each representing one barrel, were taken at random, tested, and the 

 ligures tabulated as shown liy the accompanying diagrams numbers 1 and 2 and 

 l)y Table I. 



Table I. — HhoiDinrj the variations from ihe mean of 200 hreahs of cacli of the 

 four sets of briquettes made by the testers. 



Tester, 



Neat (200 each). 



Mortar, 1 to 3 (200 

 each) . 



7-day. 



28-day. 



7-aay. 



28-day. 



A - 



502.4 

 56S.8 

 534. 6 

 32.2 

 ±6.0 



601.8 

 641.3 

 621.6 

 19.8 

 ±3.2 



143 

 164 

 153.5 

 10.5 

 6.8 



220.6 



235.3 



228.0 



7.4 



3.2 



B 



Mean 



Difference 



Per cent - 





Increase from 7 to 28 day tests. 





Neat." 



Mortar, 1 to S."- 



A. 



B. 



A. 



1 

 B. 





99.4 

 19.8 



74.4 

 13.1 



77.6 

 51.3 



71.3 

 43.5 







•Increase desired by specifications; 20 per cent. 

 I* Increase desired by specifications; 57 per cent. 



The fineness (through 100-niesh sieve) varied from 94.2 to 97.3. 

 The specific gravity dried at 110° in all cases, was below 3.08 and ranged from 

 3.02 to 3.07. 



Space will not permit of discussion in detail of the methods used b_y 

 each tester, except to say that A used the automatic tamper described 

 below and applied the blows differently than did B, who used the ordinary 

 tamper; A's briquettes were placed in a wet closet, B used the damp 

 cloth; A's briquettes were also always under water, kept running for a 

 few hours each day; B siphoned the water from the pans and then 

 refilled them, thus exposing the briquettes to air for about 10 minutes 

 each time. All these differences were in accordance with specifications, 

 as the minor details of testing were indefinite enough to allow them. 



One operator, A, always obtained lower results on an average than 

 B, but B did not show the gain in strength between the 7 and 28 day 

 tests that the cement was capable of. Evidently, B's system gave abnor- 

 mally high 7-day tests, and therefore 28-day breaks showed little increase. 

 However, notwithstanding these differences, the variation between the 

 samples themselves is also .clearly evident. 



