81 
Still, from the experiineutS of Mr. Francis, it seems to bo certain that 
Kyanizing \\ ill give better results when the timber is exposed to air than 
when placed underground. This results very likely from the sublimate 
being gradually dissolved and washed out. It might bo prevented 
probably by first drying' the treated t imber and then giving it a coating 
Of dead oil. On the ends at least . 
(."5) Chloride of Zinc. — The use of chloride of zinc for the preservation 
of timber was patented by Burnett, in England, in the year 1838. 
Chloride of zinc is prepared by dissolving metallic zinc in hydro- 
chloric acid. In its most concentrated form it contains 32 per cent, of 
zinc, but generally only 25 per cent. The specific gravity of a solution 
of this strength is about 1.6. It is sometimes made from zinc skim- 
mings, and is then liable to contain free hydrochloric acid and chloride 
of iron ; the first, like nearly all free acids, reduces the strength of the 
timber, while the second reduces the value of the solution as an anti- 
septic. 
Chloride of zinc has the greatest affinity for wood fiber, and is hygro- 
scopic, both being qualities which increase its value as a preservative. 
It is also a very strong antiseptic. Burnett at first recomnended to 
use a solution of 1 part (by volume) of concentrated chloride of zinc to 
5!) parts (by volume) of water. In Germany stronger solutions were 
frequently used, 1 in 30, 1 in 24, and in one case even 1 in 11 parts. But 
it was found, as in the case of corrosive sublimate, that by using these 
stronger solutions the quantity of zinc absorbed by the wood was not 
proportionally increased, because such solutions would not so readily 
enter the cells, and that some portions of the timber received an ex- 
cessive amount of the zinc chloride, while others received little or none. 
The presence of an excess of chloride of zinc, moreover, seems to injure 
the fiber, causing brittleness in the wood, and to prevent these conse- 
quences the strength of the solutions on German railroads has been 
reduced to 1 in 50, or 1 in 60. 
In this country solutions of 2 in 100 and 3 in 100 were used at first 
(Erie Railway Company). On the Philadelphia ami Western Railroad 
the solution used contained 5 or in 100; on the Philadelphia and 
Reading Railroad, 3| in 100; on the Havre de Grace Bridge, 1.12 in 100. 
At present the solutions generally used have a strength of 1.9 or 2 in 100. 
The strength of solutions is generally measured by the areometer; but 
the specific gravity of the solutions of zinc chloride changes so rapidly 
under changes of temperature that errors are unavoidable, unless proper 
corrections for temperature are made. 
The weight of concentrated chloride of zinc, which was absorbed from 
a solution of a strength of 1 in GO, was found to be as follows on the 
railroads of Hanover, Germany : 
100 cubic feet of Oak absorb 22 pounds of concentrated chloride of 
zinc. 
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