461 



appears to the author to have been the difficulty of making the join- 

 ings sufficiently firm to bear the necessary pressure, and at the same 

 time capable of being easily disunited for the purpose of making any 

 new arrangement of the parts ; for in both these respects, as well as 

 in other points, the usual conical joints of glass are very objection- 

 able. 



In Mr. Austin's construction, all the parts are fitted together by 

 plane surfaces, which have the advantage, not only of being easily 

 formed, but of fitting each other in any order of combination in which 

 it may be thought convenient to place them. For this purpose, each 

 part of the apparatus, where there is need of a joint, is originally made 

 by the glass-blower to terminate in a flat, thick, circular plate of 

 glass of a given diameter, that is larger than the neck to which it is 

 attached. 



The flat terminations of all the parts being then ground perfectly 

 plane, any two may be applied together, and clamped by a proper 

 system of collars and screws, with the certainty of fitting, without 

 regard to any inequality of the perforations in each, through which 

 the communication between the vessels is thus established. 



The clamps employed by the author for connecting his apparatus, 

 consist of two flat circular collars of brass, just large enough to admit 

 the circular flat flanches to pass through them, and a pair of maho- 

 gany collars of smaller dimensions, so as to fit the necks after they 

 have been sawn in two. The brass collars, having been first put upon 

 each vessel, are prevented from returning by the interposition of the 

 wooden collars, and are then screwed together by a suitable number 

 of screws. In rendering these joints perfectly secure, it is necessary 

 to turn all the screws with nearly equal force ; and it may sometimes 

 be expedient to moisten the surfaces of glass that are applied to each 

 other when any great degree of condensation is required. 



The tube through the piston terminates, at its upper extremity, in 

 a small cup, which is the segment of a sphere, and contains a plane 

 convex lens, ground to the same radius, and fitting so as to perform 

 the office of a valve. A similar valve is placed between the barrel 

 and the receiver, and another as safety-valve at the top of the receiver, 

 with a spring and screw to regulate the force of condensation that 

 may be applied. 



Since the motion of the barrel on the piston is required to be per- 

 formed with extreme steadiness, it is firmly attached by strong collars 

 to an iron sliding-bar, guided by a dove-tail groove of brass, fixed to 

 an upright pillar that stands on the platform, to which the first re- 

 servoir and piston are attached, so as to avoid all possibility of lateral 

 motion that might destroy the apparatus. 



The author observes, that if the undermost vessel, instead of being 

 open as a reservoir for air to be condensed in the uppermost, be closed 

 at the bottom, it will be exhausted, so that the same instrument serves 

 the purpose of an air-pump as well as a condenser. 



