cements, shellac

Значение термина cements, shellac в knolik

1. Shellac, made up into sticks of the size of a lead pencil, is frequently sold as a cement which will resist water, acids, oils, etc., and it answers very well. Sometimes it is mixed with very fine powders, either to give it body, or to colour it. Zinc white or plaster-of-Paris may be used to make it white; ivory black, for black; brickdust, red ochre, and vermilion for different shades of red. The objects to be cemented together are first warmed till they melt the shellac brought into contact with them. This is very good to cement broken glass, porcelain, etc., especially as the objects are again ready for use immediately when cold; but it is not adapted for flexible objects, as it cracks. It will not withstand heat or alcohol, which softens the shellac. Shellac is soluble in alcohol, when it forms what is known as Chinese glue. It is also soluble in wood naphtha. Contrary to published statements to that effect, shellac does not form as strong a cement when in the state of solution as when melted by heat. Instead of using alcohol or benzine, a watery solution of borax may be used for dissolving shellac. Take of borax, 100 parts; rain (or distilled) water, 2250 parts; heat to boiling, and while stirring, gradually add powdered shellac, 300 parts. When dissolved, strain through muslin and preserve. This forms a waterproof varnish. Paper soaked with this is waterproof, and resembles parchment. Shellac makes the best black cement for articles of jet. It is made black by smoking it in the flame of a lamp or candle.
2. Hoenle's. - Shellac, 2 parts; Venice turpentine, 1; fuse together and form into sticks.
3. It is sometimes necessary to pulverise shellac. A correspondent of the 'Druggists' Circular' has devised the following method: "Enclose the shellac in a strong, closely-woven piece of cloth, at first compressing the folds rather tightly, but gradually relaxing them. Then, after placing the bunch, which j must be held in position with the hand, upon a solid block or smooth counter, the strokes of a heavy iron pestle are applied, gently at first, while the bunch is kept moving from side to side, so as to expose every part to the strokes of the pestle. After the large, sharp pieces are broken, the strokes are increased in velocity and power, with wonderful effect upon the resin, and but little injury to the cloth. In this way shellac may be reduced to granular form sufficiently fine for pyrotechnic purposes at very short notice, and to an almost impalpable powder in a comparatively short space of time. To produce this result, however, it is necessary to wield the pestle forcibly, and then from time to time separate the finer particles from the coarser by sifting."

Рядом со словом cements, shellac в knolik