ENGINEERING AND AECniTECTUEE. 559 



hard and brilliant, having the formula As s + 1 aq. If kept at 392° for some 

 time, and then raised to 402°, the liquid becomes pasty, and at leugth forms a 

 nacreous white mass of, As 0^ + aq. 



The different hydrates, heated to a dull red heat, give the anhydrous acid, which 

 is quite inert, being iusoluble in water, ammonia, <ic, and not reddening litmus. 

 It gradually liquefies. 



Kopp found that if the bauds be exposed to the arsenic acid, they at length 

 swell considerably, and serious symptoms may be produced, washing with lime 

 water seems to counteract its effects ; the acid could be detected in the excretions, 

 and although no alteration in general health was observed, a very visible in- 

 crease took place in the weight of the body. 



Phosphoric Acid — Reissig has giv^u a modification of Reynoso's process for 

 the determination of this acid by means of tin ; the acid beiug separated from 

 the oxide by means of sulphuretted hydrogen, and determined by magnesia and 

 ammonia. The process seems to give excellent results, and to be free from some 

 of those objections, which render Reynoso's method inapplicable. Ch. G. 331. 



B.C. 



ENGINEERING AND ARCHITECTURE. 



PRESERVATION OF TIMBER. 



Plans for the preset ration of timber have frequently attracted the attention of 

 men of science, as wood is the most common material used in the arts, and 

 from the acids contained in the sap, the decomposition of the woody fibre 

 speedily commences, where these remain after the vital principle is extin- 

 guished by felling the tree. The method employed to eradicate the sap in the 

 ordinary way is by cutting the tree into planks, and exposing the surface of such 

 to the action of the atmospheric air during the heat of Summer. It is found that 

 accordiug to the climate, from one to two years' exposure, render planks sufficiently 

 seasoned or free from sap, but for large beams, joists, or girders, three or four 

 years, or even a longer time, is necessary. Expensive means have been adopted 

 in England, France, and on the continent of Europe, to imitate this natural process of 

 drying, by placing the beams and planks iu a large chamber of wood or metal and 

 passing a current of air through the chamber by means of a fan at a heat consider- 

 ably more elevated than the natural temperature. This system, although a very 

 good oue, involves too great an expense to render its adoption universal; and the 

 joist or plank has to remain from two to three, or eveu four weeks under this 

 action of hot air, before it is fully seasoned. Another and greatly simpler plan, 

 adopted with some success, is by laying the trees, wheu fresh felled, in a running 

 stream, when it is found that, after smiie weeks of immersion, the current has 

 washed out the sap from the minute pores, and substituted the water •>( the 

 stream. 



The principle adopted iu Mr. Ryan's patent process was the exhaustion, by 

 means of an air pump, of a large cylinder, into which the wood to be seasoned 

 was placed, and when fully exhausted, a solution of corrosive sublimate (chloride 

 of mercury.) was allowed '" flow in and enter the pores. Another process adopt- 



