On a Method of determining the Specific Gravity of Liquids. 255 



glass. Now the water will stand exactly at the top of the tube E, 

 and the liquid exactly at the top of the tube A ; and as the two 

 columns of liquids are supported by the same atmospheric pres- 

 sure, the specific gravities or densities of the two liquids will be 

 to each other inversely as the heights of their respective columns. 

 The heights of the respective columns being read oiF to inches 

 and tenths of inches, the quotient arising from the division of 

 the length of the column of water by the length of the column 

 of liquid will give the specific gravity of the liquid at the tempe- 

 rature of observation, that of water being imity. The specific 

 gravity of the liquid may thus be readily found true to three 

 places of figures, and, by using a hand vernier, to four places of 

 figm'es. The allowance necessary to be made for the curvature 

 due to cohesion, as well as the method of reducing the specific 

 gravities to mean temperature, are too well known to require 

 any explanation in this place. 



It will be observed that it is not at all requisite that the fluids 

 at A and E should stand at the same level ; and it will be further 

 observed, that the truth of the indications is not at all vitiated 

 by the pressure of the vapour which may arise from the liquid 

 in the tube AB, inasmuch as this additional pressure would act 

 equally on both liquids. As the specific gravity of the liquid 

 depends solely upon the relative heights of the columns A K and 

 E N, it matters not what quantity of liquid may have entered 

 the tube. After the observation has been made, the liquid 

 may be discharged from the tube, AB, by simply elevating the 



In order to economize, when desirable, the quantity of liquid 

 employed, the following artifice may be adopted : — In the place 

 of pouring the liquid into the glass G, let it be poured gradually 

 into the mouth of the tube as required, whilst the jar F is being 

 slowly depressed. Proceeding in this way, about an ounce 

 weight of the liquid will be sufficient for determining its specific 

 gravity. 



The bendings at A and E are not strictly essential to the con- 

 struction of the instrument, being introduced rather to facilitate 

 the manipulation than to contribute to the delicacy of the indi- 

 cations. When the tubes are straight at their lower extremities, 

 two glass tubular gauges may be used, terminating at their lower 

 extremities with fine points, and sliding through rings of india- 

 rubber fixed at the upper portions of the tubes B and C. In 

 this case the graduated tubes are depressed until their fine 

 points just touch the surfaces of the liquids in the vessels F and 

 G, and then the heights of the respective columns are read ofi" as 

 before. 



I have used this instrument for some time, and compared the 



