STATICAL BLOW PIPE. ipl 



nal part of the apparatus will hare no communication with 

 the external air, except through G or F, and the mercury will 

 stand on a level on both sides of A. But if the mouth be ap- 

 plied at G, and air blown in, it will be emitted again at F, with 

 a velocity which will be greater the greater the pressure ; but 

 it will not be in the power of the operator to carry this pres- 

 sure beyond a precise and steady limit. For the first effect 

 will be to depress the mercury within the tube A, and at the 

 same time to elevate the outer column or ring ; and as soon 

 as the difference between the heights of the internal and ex- 

 ternal mercury shall have become equal to that of a column of 

 mercury, having the same base as that of the internal part of A, 

 any farther effort will only cause A to ascend > and as soon as 

 this ascent shall have carried the lower rim nearly to the height 

 of the internal mercury, the air will make its escape through 

 the mercury, by means of a notch made in the rim to determine 

 the place of escape. 



Chemists will perceive, that though this instrument pos- 

 sesses facility and precision of action, and is rendered a snug 

 portable apparatus by a cylindrical cap which covers the whole 

 by screwing on at EF. j yet in point of invention it cannot claim 

 to differ much from the modern gas holders. You have 

 proved to us, on a former occasion, (Journal, quarto series, 

 H. 35.) that the difference of 4-tenths of an inch of mer- 

 cury was as much as blowing by the mouth can support or 

 maintain ; and this blast is sufficient for all the purposes of mi- 

 neralogy and glass blowing. It may also be noted, that a re- 

 action blow pipe, having a packed piston to re-act in a cylinder, 

 and, I believe, another working piston with a valve and proper 

 fittings in the same cylinder, was made many years ago by the 

 celebrated Ramsden. But his compounded apparatus differs 

 in many respects from the subject of the present description. 

 I am, Sir, 

 • * Your obliged Reader, 



C. L. 



VII. 



