for the Uft; of ArUJls, MdnufaSlurers, &c. 119 



life a little finely-waflied colcothar mixed with water for the 

 cutting material, applied between the tool and the lens. 



VI. mite of Eggs 



mixed up with a little quieklime (or a bit of chalk burnt in a 

 common lire and pounded) makes a pretty good cement for 

 glafs and porcelain. It is not abfolutely necellary that the 

 chalk be burnt, though it is generally ufed fo. 



Gum Arabic Cements. 



VIT. Gum arable diflblved in as fmall a quantity of water 

 as may be, and dduted to a proper confifience with gin or 

 any proof fpirit, forms a very ufeful cement for all purpofcs 

 where gum water is commonly ufed, the fpiiit prcferving it 

 from bccomina: putrefcent. As the fpirit evaporates, more 

 fhould be added. It fliould be (tirred and mixed together at 

 the time of ufmg. 2. If plaiftcr of Paris be added to gum 

 water, it makes a^'cment ufeful to ladies in fiUigree works. 



VIII. Gum annnoniai: added to the folution of gum arable 

 in proof fpirits very much improves the cement. It anfwers 

 very well for joining broken glafs and porcelain articles of 

 ornament. 



IX. A fne Iranfparent Glue. 



Shreds or parings of vellum or parchment, boiled for a 

 fufficient length of^time in foft water, diffohe at laft into a 

 very tranfparcnt glue. White leather, that is, (kins drcflcd 

 vit'h alum inllcad of being tanned, will anfwer the fame end. 



Iflnglif Cements. 



X. A ufeful cement is made of this fubftance by either 

 diflolving it in anv proof fpirit by heat, or by adding to it, 

 when dilfolved in water, an equal cjuantity of alcohol. 



XI. An improved cement may be made by adding to the 

 ifinglafs, previous to its folution in proof fpirits, one third 

 part of its weight of gum ammoniac. Expofe the mixture to 

 a boiling heat until the ifmglafs and gum are diffolvcd, and 

 until a drop of the compoliiion becomes (lift' inflanlly as it 

 cools. It will at any future time melt with a degree of heat 

 little exceeding that of the human body, and, in confcciucnce 

 of fo foon becoming (lift" on cooling, forms a very valuable 

 cement for manv purpofes, particularly for the very nice and 

 delicate one of fixing on the antcimae, legs, fee. ot infe<5ls in 

 cabinets of natural hiflory. 



The caiy melting of this cement is no objci'^ion to its ufe 



in cafes where the'articlcs thenifclvcs may afterwards be ex- 



^ofcd to moderate heat; for it owes thl* property only to the 



11 4 jjrefcucc 



