680 



PYROMETER 



is fully set agoing, the stopcock upon the gas-pipe is opened ; and after it is finished, 

 it must be shut. The fire should be supplied with fuel at first, but after some time 

 the gas generated keeps up the distilling heat. The charcoal is allowed to cool during 

 5 or 6 hours, and is then taken out through an aperture in the back of the chest, 

 which corresponds to the opening u, fig. 1696, in the brickwork of the furnace. 

 About 60 per cent, of charcoal may be obtained from 1 ,000 feet of fir- wood, with a 

 consumption of as much brush-wood for fuel. 



A new mode of distilling wood and producing this acid has been introduced by 

 Mr. W. H. Bowers, of Manchester. In the rectangular retort which is used there are 

 two revolving drums, one at each end. On these drums are endless chains ; on these 

 chains there is formed a flat surface by means of bars laid across. A hopper supplies 

 this surface with the sawdust or other material to bo heated. The surface is Bome- 

 what inclined. A very small engine is used to set the endless chain in motion. The 

 sawdust is carried from the upper end of the retort to the lower, during which time 

 it is exposed to heat and becomes distilled. At its lower end, as it is turning over the 

 drum, it falls in a carbonised state into water. The vapours are carried away by 

 pipes, as in the usual method, and the water-joint at the lower part of the retort 

 prevents any escape in that direction, whilst the thickness of the mass of sawdust 

 passing into the retort readily prevents any from passing out there. It is said that 

 one retort can do the work of five of those made on Halliday's plan with the screw. 

 Two of them produce with slow motion 2,500 gallons of acid in six days. The 

 motion may be increased at will, and heat regulated accordingly. There are scrapers 

 to prevent charcoal clogging the bars forming the inclined plane, and the apparatus 

 does not require to be stopped for any purpose of cleansing. It feeds and discharges 

 continuously, from month to month. 



Sawdust, wood-turnings, small chips, spent dye-wood, and tanners' bark, peat, and 

 duch like ligneous and carbonaceous substances, are distilled, and the carbon discharged 

 as shown. 



It is believed also that the distillation is effected more rapidly, and the gases more 

 directly removed by this method, than by any other. 



Fig. 1698 is a longitudinal section taken through the middle of the retort or 



1698 



rectangular vessel a,a,a;b,b are the revolving drums on which the endless chain e, e, e, 

 revolves ; /, / are cross-bars or scrapers ; g, g, are tubes to convey the gases, one from 

 the lower and one from the higher point of the moving plane ; h is a hopper filled 

 with sawdust and other material to be distilled ; the supply is regulated by two 

 small cog-wheels i, i ;j, the fire-place ; k, k, the flues ; m is "a cistern showing the level 

 of the water and the carbon falling into it, the lower part of the retort dipping 

 into it. See ACETIC ACID ; CREOSOTE. 



PYROLITHE. See K\ Pl.oM vr, AGENTS. 



PYROIiUSlTE. Native peroxide of manganese. See MANGANESE. 



PYROMETER. A n instrument employed to measure temperatures which are too 

 high to be determined by any thermometer. Some pyrometers have been constructed 

 of bars of metal ; the rates of expansion of which are known, and by which, therefore, 

 any high degree of heat could be, with some precision, determined. The pyrometer 

 of Wedgwood was formerly much employed; but it is a very defective instrument. 

 It consists of two slightly convergent pieces of copper, between which a small cylinder 



