130 VETERINARY HYGIENE 



demands that, when sifted through a standard sieve having 2500 

 holes to the square inch, there shall not be more than one-half per 

 cent, by weight of residue; when sifted through a sieve having 

 5776 holes to the square inch there shall not be more than 5 per 

 cent, residue ; and when sifted through a sieve having 10,000 holes 

 to the square inch there shall not be more than 12 per cent, of 

 residue. 



The following are the principal tests for Portland cement : 

 The Time Test, which is carried out by making a pat of neat cement 

 gauged with the minimum of water at 60 Fahr., and placing on 

 a glass slab. The pat of cement should not commence to set in less 

 than eight minutes, nor take longer than 5 hours to set. 



The Expansion and Contraction Test, which is carried out in 

 a Faija apparatus, in which a pat of cement is submitted to moist 

 heat and warm water at temperatures of 110 and 120 Fahr. 

 respectively, when it should show no signs of cracking nor of 

 expansion after 24 hours. 



The Test for Tensile Strength, which is the most important, is 

 carried out by forming briquettes of neat cement in a metal mould 

 to form a double dove-tailed block which will fit into the jaws of the 

 testing machine. The block should be gauged with the minimum 

 of water on a sheet of glass or other non-porous substance, placed in 

 water for 24 hours after gauging, and on being tested with the 

 machine should have an average tensile strength of not less than 

 350 Ibs. per square inch after 3 days, 450 Ibs. after 7 days, and 

 550 Ibs. after 28 days from the time of making the briquette. 



Portland cement should be kept in a dry store. It should not 

 be purchased in large quantities, which would involve its being 

 stored for more than about 8 weeks, as it will draw damp and set 

 in the sacks. 



Cement Mortar. Cement mortar for building purposes is com- 

 posed of about three parts clean sharp pit sand, or river sand, and one 

 part Portland cement, mixed with clean water free from organic 

 matter or other impurities. It must be used fresh as it sets rapidly. 

 Mortar left over at the end of a day must not be mixed with fresh 

 material. 



Cement Concrete for the foundations of walls, retaining walls, 

 &c., is composed of an " aggregate " consisting of clean broken 

 stones, bricks or large gravel, clean sharp sand and Portland cement 

 mixed with clean water. The proportions of foregoing vary with 

 the nature of the work and the class of aggregate and quality of 

 cement used. For ordinary foundations the following is 

 recommended : 



