407 



MISCELLANEOUS INTELLIGENCE. 



§1. Mechanical Science. 



1. Dr. Mitchell's Method of working Caoutchouc. — Soak the gum 

 elastic in sulphuric ether, until soft and nearly inelastic, which in 

 good ether will take from ten to twenty-four hours. Then if it is a 

 pliite, cut it with a wet knife or parallel knives, into such sections, 

 or sheets, or shapes, as may be desired, and suffer them to dry ; or 

 if a bag, apply a pipe or stop-cock, and inflate with the mouth ; 

 if the bag should expand equally, inflate rapidly, but if un- 

 equally, proceed more slowly and with occasional pauses. By such 

 means a bag may be made so thin as to become transparent and 

 light enough to ascend when filled with hydrogen. By graduating 

 the extent of inflation, a sheet of caoutchouc of any given thickness 

 is produced. If for blow-pipes, or other purposes for which it is 

 desirable that the bags should possess contractility, let them be 

 inflated to the desired size, and after an hour let out the air. Ever 

 after they will suffer as great a degree of extension, and again con- 

 tract. If permanent sheets are wanted, the inflated bags are to be 

 hung up until dry, after which no sensible contraction will ensue. 



Bags softened by ether maybe stretched readily by the hand, over 

 lasts, hat-blocks, or other moulds, so as to assume the shape desired, 

 and may be so applied to a variety of useful purposes. In the form 

 of straps and twisted strings, its elasticity offers many useful appli- 

 cations. It is easily formed into tubes to connect apparatus, &c. 



Some of the bags have been extended to six feet in diameter ; one 

 of these being filled with hydrogen, escaped, and was found 130 

 miles from the place. A bag, originally the size of an English wal- 

 nut, was extended until 15 inches in diameter. 



Dr. Mitchell states, that oil of sassafras softens caoutchouc so 

 that it can be applied with a brush, and that upon drying by expo- 

 sure to air, it becomes again. simple elastic caoutchouc. Many ap- 

 plications of it as a varnish, in this state, are suggested. — Franklin 

 Journal^ v. 122. 



2. Force of Dravght of Carriages. — The following results upon the 

 draught of carriages are by Mr. Bevan, and appear in the Philoso- 

 phical Magazine. — "The actual /orce o/ draught of carriages upon 

 common roads has become a subject of interest and importance, as 

 it relates to the principles erf conveyance by rail-roads, and more so 

 as it demonstrates the importance of attention to the surface of the 

 road. I, therefore, take the liberty of sending you the results of 

 some experiments of mine on that subject, conducted with consider- 

 able care, in August, 1824. ' 



** These experiments were all made or reduced to roads perfectly 

 level or horizontal, to separate the mechanical force due to the in- 



