76 Intelligence and Miscellaneous Articles. 



May 17th. — Mr. Griffiths on the manufacture of working of glass. 



May 24th. — Mr. Carpmael on the manufacture of covered buttons. 



May 31st.— -Mr. Snow Harris on the laws and nature of electrical 

 attraction. 



June 7th. — Mr. Faraday on Hullmandell's mode of producing 

 designs and patterns on metallic surfaces. Conclusion. 



XVI. Intelligence and Miscellaneous Articles. 



NEW EXPERIMENTAL RESEARCHES ON CAOUTCHOUC. BY 

 ANDREW URE, M.D., F.R.S. &C. 



THE specific gravity of the best compact Para caout- 

 chouc, taken in dilute alcohol, is 0*941567 



The specific gravity of the best Assam is 0"942972 



„ „ Sincapore 0"936650 



Penang 0-919178 



In the process of making the elastic tissues*, the threads of 

 caoutchouc are first of all deprived of their elasticity, to prepare 

 them for receiving a sheath upon the braiding machine. For this 

 purpose they are stretched by hand, in the act of winding upon the 

 reel, to 7 or 8 times their natural length, and left two or three 

 weeks in that state of tension upon the reels. Thread ^hxi.'a inelastic - 

 ated has a specific gravity of no less than 0"948732 ; but when it 

 has its elasticity restored, and its length reduced to its pristine state, 

 by rubbing between the warm palms of the hands, the specific gra- 

 vity of the same piece of thread is reduced to 0*925939. This phse- 

 nomenon is akin to that exhibited in the process of wire-drawing, 

 where the iron or brass gets condensed, hard, and brittle ; while it 

 disengages much heat ; which the caoutchouc thread also does in a 

 degree intolerable to unpractised fingers, as I have experienced. 



Having been favoured by Mr. Sievier, managing director of the 

 Joint-stock Caoutchouc Company, and by Mr. Beale, engineer, with 

 two different samples of caoutchouc juice, I have subjected each to 

 chemical examination. 



That of Mr. Sievier is greyish brown, that of Mr. Beale is of a 

 milky grey colour ; the deviation from whiteness in each case being 

 due to the presence of aloetic matter, which accompanies the caout- 

 chouc in the secretion by the tree. The former is of the consistence 

 of thin cream, has a specific gravity of 1*04125, and yields, by ex- 

 posure upon a porcelain capsule in a thin layer, for a few days, or by 

 boiling for a few minutes, with a little water, 20 per cent, of solid 

 caoutchouc. The latter, though it has the consistence of pretty rich 

 cream, has a specific gravity of only 1*0175. It yields no less than 

 37 per cent, of white, solid, and very elastic caoutchouc. 



It is interesting to observe how readily and compactly the sepa- 

 rate little clots or threads of caoutchouc coalesce into one spongy 

 mass in the progress of the ebullition, particularly if the emulsive 

 mixture be stirred ; but the addition of water is necessary to pre- 

 vent the coagulated caoutchouc from sticking to the sides or bottom 

 * See " Dictionary of Arts, Manufactures, and Mines." 



