264 Chronicles of Science. [April, 



practical purposes, seems to be, in most instances, produced by the 

 attack of fungi and lichens. The mouldering of wood is distinct 

 from decay, it being merely a chemical process caused by the action 

 of water with small access of air. None of the processes invented 

 to preserve timber by chemicals are perfect. The most simple and 

 practical method is the old, bat, unfortunately, far too slow plan of 

 properly subjecting timber to the action of air and water, as prac- 

 tised in ship-building yards. A propos of the method of preserving 

 wood by impregnation with sulphate of copper, it may be interest- 

 ing to know that by an order recently issued by M. le 3Iaire de 

 Douai, the bakers of that town have been prohibited from using 

 the wood of old railway sleepers as fuel for their ovens, since many 

 of these sleepers have been impregnated with sulphate of copper, 

 and there is danger that sonie compound of copper might poison 

 the bread. 



Professor Morton has described the works at New York where 

 oxygen gas is manufactured on the large scale. The works consist 

 of retort-houses, engine-rooms, store-house, pumps for compressing 

 gas in cylinders, and a gas-holder of 26,000 cubic feet capacity. 

 The process is carried on as follows : — About 700 lbs. of manganate 

 of soda are placed in the retort, and heated to the requisite degree ; 

 superheated steam from a boiler is then admitted for about ten 

 minutes. Two equivalents of the manganate of soda and two of water 

 react upon each other, the water combines with the soda of the 

 manganate to form a hydrate of soda, the manganic acid is converted 

 into sesquioxide of manganese, containing only half the proportion of 

 oxygen, and the other half of the oxygen passes off in the free state. 

 At the conclusion of this part of the process the steam is shut off, 

 and the superheated air is admitted for about fifteen minutes, where- 

 upon the sesquioxide combines with more oxygen from the air, and 

 is re-converted into manganic acid, which again combines with soda. 

 The retorts in each furnace are charged with 700 lbs. of permanga- 

 nate of soda, and by the consumption of 2 chaldrons of coke, and 

 with the labour of three men, 25,000 cubic feet of oxygen are made 

 per day. It is now sold at 2^d. per cubic foot, compressed in reser- 

 voirs up to a pressure of 250 lbs. to the square inch. The gas is 

 of excellent quality, and very pure. 



