PRE 



PRE 



led him to a means of impregnating 

 timlier at all seasons, in winter as 

 well as spring and autumn, and in a 

 very short space of tinu' ; tliis second 

 method is applicable to wood tliat has 

 already been squared as well as to 

 the round trunk, provided it has been 

 recently felled. 



" To impregnate timber by this 

 process, the logs are placed upright, 

 and the upper extremitios are fitted 

 with an impermeable sack for the re- 

 ception of the saline solution destined 

 . to charge them ; the fluid enters from 

 above, and almost at the same mo- 

 ment the sap is seen to begin running 

 out below. There are some woods 

 which include a large quantity of air 

 in their tissues ; in this case tlie flow 

 does not go on until this air has l)een 

 expelled : once begun, it goes on 

 without interruption. The operation 

 is terminated when the fluid, which 

 drips from the lower part, is of the 

 same nature as that which is enter- 

 ing above. In my opinion, this meth- 

 od must be preferable to that by as- 

 piration. In the second mode of pro- 

 ceeding, in fact, we accomplish our 

 object by a true displacement ; al- 

 most the whole of the sap is expell- 

 ed, and the saline solution introdu- 

 ced has only to subdue or neutralize 

 the very small quantity of soluble or- 

 ganic matter which may remain ad- 

 hering to the woody tissue. By ac- 

 complishing such a displacement by 

 means of simple water, we should un- 

 doubtedly obtain results favcmrable 

 to the preservation of timber, inas- 

 much as we should have freed it from 

 almost the whole of those matters 

 which are regarded as the most al- 

 terable themselves, and the first 

 cause of rotting in timber. The ra- 

 pidity with which the fluid introdu- 

 ced is substituted for the sap which 

 it displaces, and the quantity of this ex- 

 pelled sap, which may be readily col- 

 lected, exceeds anything that could 

 have been imagined before making 

 the experiment ; thus the trunk of a 

 beech-tree, about 52^ feet in length, 

 by 33^1 inches in diameter, and con- 

 sequently forming a cube of some- 

 what more than 29 feet and a half, 



gave, in the course of twenty-five 

 hours, upward of 330 gallons of sap, 

 which were replaced by about 350 

 gallons of pyroligneous acid. The 

 liquid which penetrates in this way 

 acts so eflectually in displacing the 

 sap, that M. Boucherie says we can 

 readily procure or extract by its 

 means the saccharine, mucilaginous, 

 resinous, and coloured juices con- 

 tained in trees. It would, perhaps, 

 be possible — and I beg to suggest this 

 idea to colonial planters — to apply 

 the method of displacement to the 

 extraction of the colouring matters of 

 dye woods.'' 



PRESS FOR CIDER. The com- 

 mon press is represented in the fig- 

 ure at the head oi" the following page ; 

 a rougher press, made by means of a 

 lever, is also much used. 



PRESS FOR OILS. See Oils. 



PRESS, HYDRAULIC. "The fra- 

 ming consists of two stout cast-iron 

 plates, d, d, which are strengthened 

 by projecting ribs, not seen in the 

 section, Fig. \. The top, or crown 

 plate, i, and the base plate, d, d, are 

 bound most firmly together by four 

 cylinders of the best wrought iron, 

 c, c, which pass up through holes 

 near the ends of said plates, and are 

 fast wedged in them. The flat pie- 

 ces, e, e, are screwed to the ends of 

 the crown and base plates, so as to 

 bind the columns laterally, f is the 

 hollow cylinder of the press, which, 

 as well as the ram, g, is made of cast 

 iron. The upper part of the cavity 

 of the cyhnder is cast narrow, but is 

 truly and smoothly rounded at the 

 boring mill, so as to fit pretty closely 

 round a well-turned ram, or piston : 

 the under part of it is left somewhat 

 wider in the casting. A stout cup of 

 leather, perforated in the middle, is 

 put upon the ram, and serves as a 

 valve to render the neck of the cylin- 

 der water-tight, by filling up the space 

 between it and the ram ; and since the 

 mouth of the cup is turned downward, 

 the greater the pressure of water up- 

 ward, the more forcibly are the edges 

 of the leather valve pressed against 

 the inside of the cylinder, anS the 

 tighter does the joint become. 



639 



