SG6 Mr Meikle on the Use of a 



On the Use of a Simple Syphon as a Hydrometer. By Mi- 

 Henry Meikle. Communicated by the Author. 



XjLmong the numerous instruments for comparing or ascertain- 

 ing the specific gravities of liquids, the " pump areometer*" has 

 been for a considerable time known. This consists of a syphon, 

 having its extremities immersed in two different liquids, whose 

 specific gravities are to be compared, and having a pump or 

 syringe communicating with the upper or bent part ; so that on 

 exhausting a portion of the included air, the atmospheric pres- 

 sure raises the liquids through heights, which are inversely as 

 their specific gravities. The reason of this is obvious, and was 

 long ago particularly noticed by Boyle. In the last volume of 

 the Philosophical Magazine^ is a description of a different in- 

 strument, consisting of a double syphon, with four parallel legs ; 

 into each pair of which, a diff^erent hquid being put, with a por- 

 tion of air between, the eff^ective columns compressing that air 

 will be inversely as their specific gravities. .This instrument 

 possesses the remarkable property, that if the bore of the tube, 

 however narrow, be uniform, its indications will be entirely free 

 from capillary action ; because both extremities of the same 

 liquid being equally aff'ected by capillary attraction, the diff'er- 

 ence of their heights, or the effective column, is not altered 

 thereby. 



It appears, however, that, when the liquids are transparent, 

 the syphon may be applied in a still more convenient form than 

 either of those just mentioned, though, to avoid capillary action, 

 the tube in this, as well as in the pump areometer, must not be 

 narrow. Thus, if the legs of a simple glass syphon be immer- 

 sed in different liquids, the lengths of the columns, depressed 

 by the included air, will be inversely as their specific gravities. 

 The vessels containing the liquids only require to be transpa- 

 rent, such as glass bottles or jars. Any scale of small equal 

 parts may be attached to the tubes ; but it will be still simpler, 

 and more convenient, for corrosive liquors to graduate the tubes 

 themselves ; for, in proper hands, a glass tube is as easily divided 

 into equal parts as any thing else. 



But with the assistance of a little calculation, the simple 

 syphon may be used for comparing the specific gravity of an 



