^42 VARNISHING. , 



litharge, for every pint of oil, till the oil has dis- 

 solved them; then put a pound of bird-lime, and 

 half a pint of the drying oil into a pot of iron or 

 copper, holding about a gallon; and let it boil 

 gently over a slow charcoal lire, till the bird-lime 

 ceases to crackle; then pour upon it two pints and 

 a half of drying-oil, and boil it for about an hour 

 longer, stirring it often with an iron or wooden 

 spatula. As the varnish in boiling swells much, the 

 pot should be removed from the fire, and replaced 

 when the varnish subsides. While it is boiling, it 

 should be occasionally examined, in order to deter- 

 mine whether it has boiled enough. For this pur- 

 pose, take some of it upon the blade of a large 

 knife, and after rubbing the blade of another knife 

 upon it, separate the knives; and when, on their 

 separation, the varnish begins to form threads be- 

 tween the two knives, it has boiled enough, and 

 should be removed from the fire. When it is almost 

 cold, add about an equal quantity of spirits of tur- 

 pentine; mix both well together, and let the mass 

 rest till the next day; then having warmed it a 

 little, strain and bottle it. If it is too thick, add 

 spirits of turpentine. This varnish should be laid 

 upon the stuff when perfectly dry, in a lukewarm 

 state; a thin coat of it upon one side, and, about 

 twelve hours after, two other coats should be laid 

 on, one on each side ; and in twenty-four hours the 

 silk may be used. 



Mr. Blcmchard's Var7iishfor Air-balloons. 



Dissolve elastic gum (Indian-rubber), cut small, 

 in five times its'*weight of spirits of turpentine, by 

 keeping them some days together ; then boil one 

 ounce of this solution in eight ounces of drying 



