140 THEORY OF CONSTRUCTION AND SCIENTIFIC DESCRIPTION 



surface is not in contact with the piston, is filled with tow, or some 

 other soft material of a similar nature ; the material thus inserted has 

 a twofold use ; in the first place, when saturated with sweet oil, it 

 diminishes the friction that necessarily arises, when the piston is 

 forced through the ring mm; and in the second place, it prevents 

 the admission of any extraneous substance, which might increase the 

 friction or injure the surface of the piston, and otherwise lessen the 

 effects of the machine. 



The packing here alluded to, is confined by a thin metallic annulus, 

 neatly fitted and fixed on the top of the cylinder, the circular orifice 

 being- of sufficient diameter, to admit of a free and easy motion to the 

 piston . 



If a cylinder thus furnished with its several appendages be placed 

 in the frame, and the whole firmly screwed together, and connected 

 with the forcing pump, as represented in fig. 1, the press is completed 

 and ready for immediate use ; but in order to render the construction 

 still more explicit and intelligible, and to show the method of con- 

 necting the press to the forcing pump, let jig. 8 represent a section 

 of the cylinder with all its furniture, jr^. 3. 



and a small portion of the tube im- 

 mediately adjoining, by which the 

 connexion is effected. 



Then is FF the cylinder; D the 

 piston; the unshaded parts oo the 

 leather collar, in the folds of which 

 is placed the copper ring pp, dis- 

 tinctly seen but not marked in the 

 figure; mm is the metal ring by 

 which the leather collar is retained 



in its place ; nn the thin plate of copper or other metal fitted to the 

 top of the cylinder, between which and the plate m m is seen the soft 

 packing of tow, which we have described above, as performing the 

 double capacity of oiling the piston and preventing its derange- 

 ment. 



The combination at wx, represents the method of connecting the 

 injecting tube to the cylinder : it may be readily understood by in- 

 specting the figure; but in order to remove all causes of obscurity, it 

 may be explained in the following manner. 



The end of the pipe or tube, which is generally made of copper^ 

 has a projecting piece or socket flanch soldered or screwed upon it^ 

 which fits into a perforation in the side or base of the cylinder, accord- 



