LIME AND CEMENT INDUSTEIES 747 



HAND WORK 



On a metal or thick glass plate five sheets of blotting paper 

 soaked in water are laid, and on these are placed five molds wetted 

 with water; 250 grams (8.75 ounces) of cement and 750 grama 

 of standard sand are weighed and thoroughly mixed dry in a 

 vessel. Then 100 ccm (100 grams or 35 ounces) of fresh water 

 are added, and the whole mass thoroughly mixed for five min- 

 utes. With the mortar so obtained the molds are at once filled^ 

 with one filling, so high as to be rounded on top, the mortar 

 being well pressed in. By means of an iron trowel 5 to 8 cm 

 (1.96 to 3.14 inches) wdde, 35 cm (13.79 inches) long, and weigh- 

 ing about 250 grams, the projecting mortar is pounded first gently 

 and from the sieve, then harder into the molds until the mortar 

 grows elastic, and water flushes to the surface. A pounding of 

 at least one minute is absolutely essential. An additional filling 

 and pounding in of the mortar is not admissible, since the test 

 pieces of the same cement shall have the same densities at the- 

 different stations. The mass projecting over the mold is care- 

 fully taken off, and the test piece placed in a box lined with zinc,, 

 which is to be provided with a cover, to prevent a non-uniform 

 drying of the test pieces at different temperatures. 24 hours- 

 af ter being made, the test pieces are placed under water, and care 

 has to be taken that they remain under water during the whole- 

 period of hardening. 



MACHINE work: 



After the mold, provided with a guide mold, has been clamped^ 

 by means of set screws, on the bedplate of the pounding machine,, 

 for each test, 180 grams of the mortar, made as above, are placed 

 in the mold and the iron follower is set in. By means of Bohme's 

 hammer apparatus, with a hammer weighing 2 kilograms, ISO- 

 blows are struck on the follower. 



After the guide mold and follower have been removed, the test 

 piece is scraped off, smoothed, taken with the mold from the bed- 

 plate and for the rest treated as for the hand work. By accu- 

 rately following the directions given pbove, hand and machine- 

 work give well concording results. In all cases of doubt the- 

 machine work is to be decisive. 



COMPRESSIVE TESTS 



In order to obtain concordant values in compression tests at 

 different stations, machine making is necessary. 400 grams of 

 neat cement and 1200 grams dry standard sand are thoroughlj^ 



