144 Mr Ven tress's ^i^^r^om^^^r. 



bottle, and B to the inverted phial. A is ground so as to fit 

 into B air-tight, and is intended for the reception of the solid. 

 B contains a glass stop-cock near that extremity into which 

 the vessel A is ground to fit. Through its perforation, the 

 vessel B is filled with water previous to each experiment. 

 Upon joining the two vessels and turning the stop-cock, the 

 water in B descends and displaces the air in A, which is made 

 to contain just as much water as the ball and stem of B. If, 

 therefore, the vessel A were empty when the water is allowed 

 to descend, the air which it contained would evidently occupy 

 the whole of the ball and stem of B ; but if a quantity of so- 

 lid matter has been introduced into A before the water is 

 allowed to descend, the air which rises into B will be diminish- 

 ed by the bulk of the solid, and the water will not fall to the 

 bottom of the stem as in the former case, but stand at a cer- 

 tain height in it. That the height at which the water stands 

 in the stem may be easily appreciated, it is graduated from 

 the bottom upwards into hundredths of a cubic inch of its 

 capacity. If, with a known weight of powder, the water 

 stood at the point marked 60 on the stem, the bulk of the 

 substance would therefore be j%%, or J a cubic inch. Know- 

 ing thus the weight of a certain bulk of the substance, we 

 have only to compare it with the bulk of the same weight of 

 distilled water, to obtain an expression for the specific gravity 

 of the substance on the usual scale. 



In the instrument which has been constructed, and which is 

 represented in the figure, the lower vessel, or rather the lower 

 vessel together with that part of the upper vessel which is be- 

 neath the stop-cock, contains 2.33 cubic inches, which is also 

 the sum of the capacities of the ball and stem. The stem itself 

 contains 1 .40 cubic inches, is long (sixteen inches,) and widened 

 into a ball at the top, the only use of which is to enable us to 

 dispense with a great length of tube, which would inevitably 

 follow from its being so small as above described, and which 

 smallness is requisite for the delicacy of the instrument. 



The construction of the instrument might perhaps be con- 

 siderably facihtated, by making the part of B (see Fig. 2.) 

 under b, of brass, with a brass stop-cock. To the neck of A 

 a brass ring might be cemented, and the two vessels made to 



