Areomieter. 115 



the exterior atmosphere, and if a few strokes of the syringe 

 be now effected, a portion of air will be pumped out of the 

 tubes, and in consequence the fluids — the mercury and 

 the water — will rise in their respective tubes. The heights 

 of the columns thus raised will be inversely as the specific 

 gravities of the liquids ; thus, in round numbers, with 

 mercury having a specific gravity of thirteen and six-tenths, 

 for one inch of column of mercury, we shall have a column 

 of distilled water measuring thirteen and six-tenths inches, 

 or for any given height of mercury that of distilled water 

 will be thirteen and six-tenths times as great ; always 

 measuring from the surface of the fluid in the beaker to the 

 top of the column standing in the tube. The measurements 

 are made with the cathetometer, by the vernier of which 

 the five-hundredth part of an inch is measurable, and 

 when the utmost attainable accuracy is required, the mean 

 of several measurements may be taken. Results are thus 

 obtained with great rapidity, and the arrangement appears 

 to promise some special advantages in comparing the 

 specific gravities of fluids through a range of varying tem- 

 peratures, as well as in the case of fluids of more or less 

 viscous character, such, for instance, as blood aud other 

 animal fluids. One point of interest in reference to this 

 mode of taking specific gravities is the fact that the 

 measures are in a certain sense absolute, for although mere 

 linear measurement, as an indication of mass, will not com- 

 pare with the decisions of the balance ; yet, on the other 

 hand, we have no corrections to*' make for the altered 

 capacity of the containing vessel following change of tem- 

 pera.ture, as in taking the specific gravity of fluids in the 

 balance by means of the ordinary specific gravity bottle. 



It is true that capillary action is an influence to be taken 

 into account in interpreting results obtained with this 

 areometer ; and it is also true that with certain fluids, as 

 with oil-of-vitriol and water for example, the one will in 

 time distil over, even at ordinary temperatures, and will 

 sooner or later vitiate the fluid with which it is compared, — 

 the water will thus distil over and dilute the oil-of-vitriol ; 

 but these are not disturbing causes of such a character as 

 to forbid the readily obtaining reliable and valuable results' 

 by employment of this instrument. As a means of demon- 

 strating, from the lecture table, the relative specific gravities 

 of different fluids, this arrangement certainly possesses very- 

 notable advantages. 



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