SCIENTIFIC NEWS. 159 



3. Gilding hy means of Zinc. 



The same intelligent and active philosopher, whose name New process 

 I forbear to mention only because I have not at this instant an of gildings 

 opportunity of asking his permission, informs me that a 

 coating of brass, formed by the precipitation of zinc upon 

 copper, constitutes the surface of the beautiful gilt trinkets 

 which at present abound in our shops, and are much supe- 

 rior ill their appearance, and cheaper in price, than what 

 were formerly made. 



The process is, Take of zinc one part and mercury 

 twelve parts, with which make a smooth soft amalgam. It 

 is better if a little gold be added. Clean the copper piece, 

 or trinket, very carefully with nitric acid. Put the amalgani 

 into muriatic acid, and add argol (by which name the crude 

 tartar is denoted in the shops). Purified tartar will not do. 

 Boil the clean copper in this, and it will be very finely gilt. 

 Copper wire, thus coated, is capable of being drawn out to 

 the fineness of an hair, though copper alone would not. 

 This wire is used for making gold lace, and for epaulets and 

 other similar articles. 



The theory of the above process appears to resemble that 

 of whitening pins; and its useful applications may probably 

 be more numerous than those which have yet been adopted. 



4. Clock of the famous John Harrison, zchich does not 

 require cleaning. 

 Ciimmings, in his Treatise on Clock and Watch Work, Harrison's 

 mentions a clock of Harrison's which was constructed to go dock without 

 altogether without oil; but he does not say by what means <^'^' 

 the necessary lubricity of its moving parts was obtained. 

 About two years ago I saw this clock in tho hands of Mr. 

 John Ilaley, Jun. The pivots of the wheels nioved on fric- 

 tion rollers of considerable diameter ; and the pivots of these 

 rollers, or rather wheels, were brass, and moved in sockets of 

 a dark coloured wood, which 1 think must have been lignum 

 vitie. Hence it should seein that the contrivance was re- 

 duced to that of rendering the surfaces of contact, where the 

 sliding or friction was to take place, as slowly moving as 

 possible, and in presenting a face which should afford a 

 softish bed, having grease in its interstices. Similar to this is 

 the practice of some mechanics, who make the bearing parts 

 of the axis of a grindstone very smooth and round, and en- 

 vclope them with a piece of bacon-skin, which is said to be 

 very useful to keep away the sandy particles, and facilitate 

 the motion for a long time without much wear. 



