40 



WELLS'S NATURAL PHILOSOPHY. 



How do yre 

 find the Spe- 

 cific Gravity 

 of a body 

 lighter than 

 water 7 



j-jg g Suppose a piece of gold -n-eighs in 



the air 19 grains, and in Tvater 18 

 grains ; the loss of weight in -water will 

 be 1; 19-7-1 = 19, the specific gravity 

 of gold. 



Fig. 8 represents the arrangement of 

 the balance for taking specific gravities, • 

 and the manner of suspending the body 

 in water from the scale pan, or beam, 

 by means of a fine thread, or hair. 



76. To find the specific 

 gravity of a body lighter than 

 water, tie it to some substance 

 sufficiently heavy to sink it, 

 whose weight in air and water 

 is known. Weigh the two together, both in air and. water, 

 and ascertain the loss in weight. This loss 

 will be the weight of as much water as is equal 

 in bulk to the two solids taken together. 

 Subtract the loss of the heavy body weighed 

 by itself in water, previously known, from the loss sus- 

 tained by the combined solids. The remainder will be 

 the weight of as much water as is equal in bulk to tho 

 lighter body, Di\"ide the weight of the lighter body in 

 air by this remainder, and the quotient will be the spe- 

 cific gravity required. 



Thus, for example, let the weight of the ligliter solid be 3 ounces, and that 

 of the heavier soUd 15 ounces. Let the weight which the two together lose 

 when submerged in water, be 5 ounces, and let the weight which the heavier 

 alone loses when immersed be 1 ounce. Subtracting the loss of weiglit of tho 

 heavier body, in water, 1 ounce, from the combined loss of the two in water, 

 5 ounces, we have 4 ounces as the weight of a mass of water equal in bulk to 

 the lighter body. But the weight of the hghter body in air is 3 ounces; 

 3-j.4=0.75=:|-. It will, therefore, weigh three quarters of its own volume 

 of water, or have a specific gravity 0.75. 



77. The specific gravity of Liquids may also be found by ths 

 balance in the following manner : Weigh a sohd body 'n water, 

 as well as in the liquid whose specific gravity is tn be de- 

 termined ; then the lo.ss in each case will be the re«;pective 

 weights of equal bulks of water and hquid. We have, there- 

 fore, the following rule : 



78. Divide the loss of weight in the liquid by the loss 



How may we 

 find the Spe- 

 cific Gravity 

 directly by the 

 balance ? 



