LIME AND CEMENT INDUSTEIES 729 



Adhesion 



This test Is usually applied by taking two pieces of glass 4x8 

 inches and 1 or li inches thick. Mix the mortar and place it 

 between them, wdth the slabs at right angles, and press the mortar 

 out into a layer 1 inch thick. The sample is allowed to stand 

 24 hours under a damp cloth, and then immersed in water. They 

 are pulled apart at end of 7 or 28 days. Better results are often 

 obtained by the use of brick and stone instead of glass. 



Permanency of volume 



Good cements should not expand or shrink appreciably in set- 

 ting. If there has been any appreciable flaw in the manufacture 

 of the cement, it will tend to expand or shrink, and disintegrate. 

 This expansion is known as ^' blowing. '^ One of the best meth- 

 ods of testing the constancy of volume of a cement is to mix it 

 with a small quantity of water, and press it firmly into a straight 

 glass lamp chimney. If any expansion takes place, it will crack 

 the chimney. By the same means shrinkage can also be deter- 

 mined, this being done by putting some colored liquid in the 

 chimney above the cement. If the latter shrinks, it will allow 

 the liquid to run down the interior of the tube. 



The expansion may take place immediately, or not show till 

 several days after the cement has been mixed, depending on the 

 rapidity of setting of the cement. 



Another convenient means of testing for constancy of volume 

 is to mix the cement with water, and make up a few ounces of 

 it into a pat 3 inches in diameter, ^ inch thick at the edge and 

 •J inch at the middle. Place this for 24 hours under a damp 

 cloth and then in water. If it shows no cracks at the edges after 

 three days, it will not be likely to blow. 



Henry Faija, in the I. civil engineers, states that he uses- 

 the following method to hasten the test. He takes a vessel 

 in which water can be maintained at a constant temperature of 

 110° or 115° E, and having a cover, under which and above the 



