2/5 On the Resilience of Materials ; with Experiments. 



The artist should contrive to charge his furnace with pieces 

 the colour of which is ground in the same vehicle, and not to mix 

 in the same hurningsome colours ground in turpentine and others 

 ground in water. The pieces must also be very carefully dried, 

 *nd must be placed in the furnace when this latter is moderately 

 warm. 



To gild Glass. 



Take of fine gold in grains . . . . 1 \ 

 of pure mercury 8 / " 



Warm the mercury and then add the gold, previously making 

 it red hot. When the gold is perfectly dissolved, pom- the mix- 

 ture into cold water and wash it well. Then press out the su- 

 perfluous mercury through linen or soft leather, and the mercury 

 v.'hich runs through (as it retains some gold) should be r°served 

 for the next opportunity. 



The amalgam which remains in the leather is to be digested 

 in warm aquafortis, which will take up the mercury, but will 

 leave the gold in the form of an extremely fine powder. This 

 powder, when washed and dried, must be rubbed up with one- 

 third of its weight of mercury ; then mix one grain of this amal- 

 gam with -three grains of gold flux (see the former part of this 

 paper, p. 271), which is to be applied in the usual manner. 



*,* In the foregoing communication borax is mentioned as an ingredient 

 ■in the composition of the fluxes. It does give them very easy fusion, but 

 we should fail in our duty did we neglect to caution artists against a profuse 

 use of this flux. It can hardly be employed in any quantity whatever with- 

 out danger to the durability of the work ; having a great tendency to efilo- 

 resce in the atmosphere. Indeed this can hardly, if at all, be prevented 

 where borax enters into the composition of colours used for painting on 

 glass. — Edit. 



XLVl. On the Resilience of Materials; u/ilh Experiments, By 

 Mr. Thomas Trkdgold. 



To Mr. Tilloch. 



Sir, — A REVious to making the experiments on the resilience of 

 timber, the results of which are given in your Number for last 

 month*, I had endeavoured to anticipate the results by the usual 

 mode of calculation, and proceeded to make some rough essays, 

 in order to try the apparatus and prepare for more correct expe- 

 riments ; as it was desirable to let the weight fall from a height 

 that would only just produce fracture, without having to make 

 successive trials, which always weaken the pieces considerably. 



In these trials I soon discovered that the calculations I had 

 made would be of no use to me whatever, although I had to- 

 • PhU. Mag. vol.li. p. 216. 



lerablv. 



