112 PRACTICAL TREE REPAIR 



About the Home and on the Farm," published by 

 a cement company. 



" Pick up a double handful of moist sand from 

 the bank; open the hands, holding them with the 

 thumbs up ; rub the sand lightly between the hands, 

 keeping them about half an inch apart, allowing 

 the sand to slip quickly between them. Repeat 

 this operation five or six times, then rub the hands 

 lightly together so as to remove the fine grains of 

 sand which adhere to them, and examine to see 

 whether or not a thin film of sticky matter adheres 

 to the fingers ; if so, do not use the sand, for it con- 

 tains loam." 



Bank gravel makes a fairly good ready-mixed 

 aggregate for concrete, although as a usual thing 

 it is not correctly proportioned, the amount of 

 sand being excessive. It is ordinarily best to put 

 some of the gravel through a quarter-inch screen 

 in order to determine what its actual composition 

 is. Then, if a deficiency of the larger pebbles is 

 indicated, enough screened gravel can be added to 

 make the proportions correct. If pure sand has to 

 be used it must be mixed at about the rate of two 

 parts of sand to one of cement, in order to approxi- 

 mate the richness of a i :4 gravel mixture. 



The various mixtures of cement, aggregates, 

 and water, which are used in making concrete are 

 grouped in two ways: according to the proportion 

 of cement to aggregates, and according to the 



