570 



THE GARDENER. 



[Dec. 



The amount of expansion in water corresponds inversely with the 

 weight of equal bulk or the specific gravity, and it has been very care- 

 fully measured by men of science. The following table gives the 

 mean results obtained by the latest observations. I have thought it 

 sufficient to set down the figures for increments of 18°, which corre- 

 sponds to 10° C.* :-- 



Temp. 

 Fahr. 



32° 

 (39° 

 60° 

 68° 

 86 c 

 104 c 



2) 



Vol. of water 

 (at 32° = 1.) 



1.01181 



1.01677 

 1.02243 

 1.02874 

 1.03554 

 1.04300 



3p. gr. of water 

 (at 32° = 1 ) 



.98833 

 .98351 



.97807 

 .97206 

 .96568 

 .95878 



It will be seen from this table that water does not expand in equal 

 proportion for different increments of heat. Thus from 50° to 68° it 

 expands about 15 parts in 10,000, from 122° to 140° it expands about 

 50 parts in 10,000, and from 176° to 194° it expands about 78 parts in 

 10,000. This fact will be found to have some importance in consider- 

 ing questions of circulation in pipes. 



In dealing with the effect of gravity on water, it must be kept in 

 mind that we have to consider only the height and not the bulk in 

 other directions. This is a law of hydrostatics, a familiar example of 

 which is that water will stand at exactly the same height in a small 

 pipe communicating with a big barrel as it does in the barrel itself 

 when it is of the same temperature in both. But, 1st, if the pipe 

 communicates with the barrel only at its bottom, and we heat the 

 water in one but not in the other, the level of the hot water will stand 

 a little higher than that of the cold, because it takes a greater height 

 of the hot water to balance the denser and heavier cold water. And, 

 2d, if the pipe communicates with the barrel both at bottom and top, 

 and we heat the water in the barrel or the pipe, but not in both, a cir- 

 culation will be set up, because now the water in both stands at the 

 same level, but the column of cold water is heavier than the column 

 of hot ; the cold is, therefore, carried down by the superior force of 

 gravity, and compels the hot to rise. The amount of force exercised 

 appears from the table given above. Thus if the water be 3 feet deep, 

 and its temperature in the pipe be 50°, and in the barrel 194°, then the 

 weight of the water in the pipe is 3 X. 999876 = 2.999628 (in grains, 

 ounces, or any other denomination), while the weight of a correspond- 

 ing column in the barrel is, in the same denomination, 3 X. 96568 = 

 2.89704. Hence if the water in the pipe weighs 2.9 oz., the corre- 

 sponding amount of water in the barrel weighs about 2.8 oz., and 



* Fuller tables may be found in any of the treatises on heat. 



