410 



AGRICULTURAL ENGINEERING 



Sandstone of a good grade is an excellent building mate- 

 rial. It has a strength of about 11,000 pounds per square 

 inch and weighs about 140 pounds per cubic foot. 



The densest and strongest stones are the most durable, as 

 a rule. A good stone will not absorb more than 5 per cent 

 of its weight of water when soaked in water for 24 hours. 



Brick. Brick is a material quite generally used over the 

 country, and when of a good quality is quite satisfactory. 

 Brick should be of uniform size, true and square, and when 

 broken should show a uniform and dense structure. Good 

 brick will not absorb moisture to an extent greater than 10 



per cent of its weight, 

 and the best will absorb 

 less than 5 per cent. 

 The crushing strength 

 of brick should exceed 

 4000 pounds per square 

 inch. 



Hollow clay blocks 

 or tile are made of the 

 same material as brick, 

 and should have the same characteristics. Clay blocks are 

 lighter than brick, and so the cost of shipping is less. They 

 cost less by volume, and more wall can be laid in a given time 

 than with common brick. 



Lime. Lime is used in mortar where the greater dura- 

 bility and strength of cement mortar are not needed. Quick 

 lime should be in large lumps and should be free from cinders 

 and dust. When slackened with water it should form a 

 smooth paste without lumps or residue. Lime mortar is 

 usually made of 1 part of lime to 2 or 3 of sand. 



Portland Cement. Portland cement is now generally used 

 in the making of mortar and concrete. It should be finely 



Fig. 260. Hollow clay building blocks. 



