160 MR J. Y. BUCHANAN ON THE 



The selected example is that of hydrometer A when immersed in distilled water, 

 and afterwards in a 4*4 gram-molecule solution of potassium chloride. 



Referring to Experiment No. 1, when working completely in vacuo, with the hydro- 

 meter immersed in distilled water, the adjustment would be such as to cause it to Hoat 

 with the stem immersed to a scale reading of C = 177 mm. 



Weight of glass and shot = W= 136-69884 grams. 



On replacing the distilled water by the experimental solution, the added weight 

 necessary to cause the instrument to float at 17"7 mm. in vacuo would he w^ 23'25860 

 grams (true). 



Weight of shot + glass + added weight = W + w= 136-69884-1- 23-25860= 159-95744 

 grams. The specific gravity would therefore be : — 



W + w 159-95744 



W 136-69884 



= 1-170144. 



On admitting air into the hydrometer (Experiment No. 3), the result would be to 

 cause the instrument to be immersed to C'= 32-2 mm. in distilled water. 



This is arrived at in the following manner : — The internal volume occupied by the 

 air is 112-493 c.c, and the density of the air was 0'001208 gram per cubic centimetre. 

 The weight would therefore be a = 0"13592 gram. 



Since O'l gram added weight produces an immersion of 10-69 mm. of stem, and as 

 the weight of air admitted is distinctly an added weight, the immersion produced by 

 0-13592 gram would be 



10-69 X 0-13592 ,,r 



= 14-0 ram. 



0-1 



Whence 17-7 H- 14*5 = 32-2 mm. 



Total weight after admission of air to hydrometer is : — 



Weight of shot -f- glass -1- air = W -t- a = 136-69884 + 0-13592 = 136-83476 grams. 



On immersing the hydrometer filled with air into the experimental liquid with a 

 similar adjustment as in the first experiment {W + tv), the hydrometer would be immersed 

 to a point short of C, since the air represents the same added weight in this case as 

 when the hydrometer is immersed in distilled water, and the same added weight would 

 not produce so great an immersion of the stem in the experimental liquid as in the 

 distilled water of lower density. Hence an addition must be made to the original added 

 weight (w) to cause the hydrometer to float at C, the 32-2 millimetres division, when 

 immersed in the experimental liquid, and the value of this addition is the diff"erence 

 between the weights of the same volume of experimental liquid and distilled water 

 represented by the volume of the portion of stem immersed when air was admitted into 

 the hydrometer while experimenting in distilled water. 



Then we have seen that the weight required to increase the displacement in 

 distilled water from C to C is the weight of the air filling the hydrometer, namely, 

 0-13592 gram. When the distilled water is displaced by the experimental solution, 



