37^ ELECTRICITY. 



To cover glass with sealing-wax in the dry way, 

 glass should be warmed gradually near the fire, and 

 when sufficiently warm, a stick of sealing-wax 

 must be gently rubbed over its surface; by this 

 means the sealing-wax is melted, and adheres to 

 the glass. As this is a troublesome operation, and 

 there is some risk of breaking the glass, the sealing- 

 wax is sometimes dissolved in spirit of wine, and 

 laid on with a hair pencil. For this purpose the 

 wax must be broken into small bits, and suffered 

 to remain in the spirit for a day or two, shaking it 

 now and then. This solution must be laid upon 

 the glass when dry and clean, by means of a hair- 

 pencil, and when the first coat of it is quite dry, 

 then a second, a third, and even a fourth coat, 

 should be applied. The best varnish for this pur- 

 pose is the amber-varnish, which, indeed, answers as 

 well as the sealing-wax, in the dry way, but it 

 must be made with great care and attention. 

 For the process of making it, see vol. ii. article 

 Varnishes. 



To make the amalgam for laying on the rubber, 

 mix two parts of quicksilver with one of tin-foil, 

 adding a small quantity of powdered chalk ; and 

 rub them together in a mortar until it becomes a 

 mass like paste. 



A better amalgam is the following: put a quan- 

 tity of quicksilver into a crucible, and heat it above 

 the boiling point of water. Also melt a fourth 

 part of zinc in another crucible. Pour the heated 

 quicksilver into a wooden box, and add the melted 

 zinc to it. Then shut the box, and shake it for a 

 minute or two. You must suffer it to remain till 

 it is almost cold, and you will find that the two 

 metals have united perfectly, forming an amalgam. 



