xt8 Memorandums, Hints, Precepts, and Recipes, 



Temporary Cements, C^c. 



Workmen are often at a lofs for fiich a cement as will 

 hold firmlv till they have no further occafion for it, and yet 

 be eafily parted when it is neceflary ; as in fixine glafs plates 

 to blocks to be ground for optical purpofes, joining metallic 

 plates to be turned in a lathe, &cc. For fuch purpofes a ce- 

 ment compoled of the following ingredients will be found to 

 anfwer well : 



III. To four ounces of refin and T-4thof an ounce of bees 

 wax melted together, add four ounces of whitening (wafhed 

 carbonate of lime or chalk) made previoufly red hot. The 

 whitening fhould be put in while yet hot, that it may not 

 have time to imbibe moiRure from the atmol'phere. This 

 makes a good cement for holding optical gUUits on the end 

 of a tnaundril while grinding, or for (imilar purpofes. 



To cement plates of metal to the chucks of a lathe in order 

 to turn them, the chuck fliould be heated, which is com- 

 monly done, by di reding the flame of a candle upon it urged 

 by a blow-pipe ; the metal fliouId alfo be heated in the fame 

 manner until they will melt the cement applied to them. 

 The pieces, being then placed in contaft, are adjuftcd cen- 

 trally while the cement cools, either bv holding a pointed 

 iWck in a fmall hole previoufly made in the centre of the 

 plate by a prick punch, or by prefling a piece of wood late- 

 rally againft it. When cold it will be held firm enouch, 

 by means of the cement, to bear being turned, and may be 

 difengaged at anv time by again heating it. 



IV. Pitch, refin, and a very fmall quantity of tallow, 

 melted together, and thickened by ftirring in dry brick-dufl:, 

 is employed by chafers of gold and filver articles to fupport 

 and hold their work. 



This inixture forms a cheap cement ufeful for manv pur- 

 pofes, as fixing fmall fteel articles on the blocks deflined to 

 hold them for poli(hing, and is much ufcd at Birmingham. 

 The proportions of the ingredients depend on the heat of the 

 weather and the particular pnrpofe in view. In winter, a, 

 larger portion of tallow is neceflary than in fummer. 



V. Shell-lac is a very llrong cement for holding metals, 

 glafs, or precious flones, while cutting, turning, or grinding 

 them. The metal, &c. fliould be warmed to melt it. 



For faflening rubv cvlinders in watches and fimilar deli- 

 cate purpofes, ihell-lac is alfo very excellent, 



Meinorandum. — Bees wax mixed with a little colcothar 

 (red oxide of iron) makes a good polifliing tool for lenses : 



uf? 



