VOL. XXXIX.] PHILOSOPHICAL TRANSACTIONS. 83 



spring G ; and the index will, at the same time, by means of the silk line, be 

 carried forward in the circle; and as the bar shortens, it will return back again; 

 the same motion will be communicated to the standard bar. The lengthening 

 the bar the iOth of an inch, will carry the index once round the brass circle, 

 which is divided into 36o degrees; therefore, if the metal lengthens the 7'200th 

 part of an inch, the index will move one degree. 



To make an experiment with this instrument, lay a bar of any kind of metal, 

 as E, on the standard bar ; then heat the standard bar to any degree of heat 

 with a lamp, and mark the degree of its expansion, as marked by the moveable 

 plate : observe also the degree of expansion of the metal k, by the heat com- 

 municated to it from the standard bar, as marked on the brass circle by the in- 

 dex : let the instrument stand, till the whole is thoroughly cold ; then remov- 

 ing the bar e, lay a bar of any other metal in its place, and heat the standard 

 bar to the same degree of heat as before, which is seen by the moveable plates 

 marking the same degree of expansion. Then the index will show the degree 

 of expansion of the second metal, as it did of the first ; and by this means the 

 degrees of expansion of different metals, by the same degree of heat, may be 

 exactly estimated. 



ji further Account of the Bones of Animals being made Red by Aliment only. 

 By John Belchier, F. R. S. N° 443, p, 299. 



In the former account, p. 7g, concerning the red bones of the hogs, Mr. B. 

 mentioned, that the colour was occasioned by bran being mixed with their 

 common food, after it had been used to clean printed callicoes ; the colours of 

 which were made, some from preparations of iron, which were the blacks and 

 purples ; others from preparations of alum, and sacc. saturni, which produces 

 the red colours ; and that madder root was used to fix these colours on the 

 cloth. To which of these preparations the colour was owing, could not then 

 be determined. Some were of opinion, that it was entirely occasioned by the 

 preparations of iron ; others, that it was the whole blended together. But 

 to clear up this point, Mr. B. made the following experiments. The first was 

 made on a cock, by mixing some of the madder root with fig-dust, on which 

 they feed. The cock dying within ]6 days after his first feeding on the mad- 

 der, he was dissected, and the bones examined, not in the least expectation of 

 finding them tinged in so small a time ; but they were found universally of a 

 red colour. So that, from this experiment it appears, that the madder alone 

 causes tliis alteration. But why the bones only are aflx-cted, must be deter- 

 mined by future experiments. 



M 2 



