answer. 



334 ON MtmSTINfi TRE DECAY OP WO#D; 



whole became a firm and solid crust ; after which the shoots 

 vere put into their places,, and beii*£ examined many jears 

 afterward, appeared perfectly sound. Any other colour 

 would probably have succeeded equally well with that 

 Lamp black which 1 employed. I do not think that lamp black, which 

 rood Sn ° tS0 IS a P ure s P ecies °f charcoal, would have answered the 

 purpose of forming a thick defensive covering so well as the 

 grosser charcoal which I used. But whatever sort of char- 

 coal is employed, it ought either to be fresh made, or heated 

 again in close vessels, so as to expel the water which it 

 greedily attracts from the air. 

 Drtins oils ex- To all compositions formed from drying vegetable oils 

 pensive. there is this objection ; that however well they may answer 



the end proposed, they arc too dear for that great con- 

 sumption, which is usually required for outside work. For 

 this and other reasons, various other substances have been 

 employed fop the same purpose. 

 Pitch does not Of these the most common is pitch, which is well known 

 to be the resinous matter melted by heat out of the pine 

 tribe of trees in form of tar, and afterward hardened by 

 evaporation. It is applied hot, and when cold, makes a 

 moderately hard varnish. It does not however appear, in 

 fact, to answer the purpose so well as might have been ex- 

 pected. The sun at first melts it, so that it runs ofl in 

 drops, or adheres to every thing which touches it; and the 

 united influence of air and water seems to make it brittle 

 and powdery like resin. Experience therefore shows it to 

 be of little value. Neither is it probable that its powers 

 would be much improved by admixture with charcoal, sand, 

 or other similar substances. Many members of this So. 

 ciety may recollect its application twenty years ago on the 

 red-deal shingled roofs of part of our market. In this 

 case it was used hot, mixed with Spanish brown, and har- 

 dened by sand sifted over it with a sieve; notwithstanding 

 which it seems to have left the wood like the unmixed 

 pitch, and, though frequently renewed, has not preventer 

 the necessity of various repairs within these last five years. 

 The original boards are now every where more or less in a 

 state of decay. 



Th# 

 / 



