272 MAKING AND BEAUTIFYING THE HOME 



says, " causes it to set." Many of our tall buildings, 

 as the " skyscraper " shown in the illustration, are made 



of concrete, built upon 

 rods of steel and wire 

 mesh. Concrete, as we 

 know, has recently come 

 into use even for build- 

 ing ships, and many 

 other different uses are 

 made of it. 



Experiment. To make con- 

 crete of various mix- 

 tures and to compare 

 properties. 



Materials: Portland cement. 

 Sand. Steel knitting nee- 

 dles. Frame with six com- 

 partments, each about i 

 inches deep, i inch wide, 

 and 10 inches long. Mix 

 sand and cement dry, 

 in proportions indicated. 



Then add water to make a pasty mass which slides easily from the 

 trowel. Make the following mixtures and pour them into the 

 frames : 



A skyscraper, built mostly of concrete. 



1 Reinforce by putting in five steel knitting needles well spaced. 



2 Instead of using sand use dark earth or loam. 



