An Invest] gallon of flexible Substances, 139 



almost instantly to form a perfect soap ; if we repeat the so.rae 

 experiment by treatini;: in a similar way, and in the same space 

 of time, any recent tallow with an alkali, scarcely shall we be 

 able to produce anv perceptible traces of soap. 



If we do not succeed in bringing a rancid fat back to its pri- 

 mitive state, we may at least retard its rancidity: a slight alka- 

 line solution seems to enjoy this property: heiiCe the practice 

 in certain countries of keeping- fresh water in cloths moistened 

 with a lixivium. 



The disposition of the rancid fats to be saponified in a few 

 minutes, niight perhaps present some useful results for soap- 

 makers : it also shows the profound alteration which they hava 

 undergone, and the different degrees by which they become 

 adipocire — time alone can operate this change, as Fourcroy 

 proved in his examination of the churchyard of the Innocents. 

 This chemist also ascertained that fat persons furnished more 

 adipocire than lean, and that the marrow of the long bones v/&% 

 converted wholly into adipocire. 



\yi.\l\\.AnInvestigation of the Pressure sustained ly the fixed 

 Supports nf flexible Substances. 



To Mr. Tilloch. 



Sir, — 1 HE formidable accident, which occurred some time since 

 from the failure of the hoops of a vat of great size, has led to an 

 inquiry respecting the strength required in structures of this 

 kind: and its results are comprehended in the following propo- 

 sitions. It must be remembered that thev are oniv correctly tme 

 upon the supposition that the resisting ])oints are ahsolutelv fixed, 

 and that in actual practice the forces will be somewhat more 

 equally divided: it would, however, be always prudent to make 

 the strength great enough for the most unfavourable supposition 

 that can be made respecting its employment. 



A. If a flexible bar, equably loaded throughout its length, 

 !>e supported at each end and in the middle by fulcrums perfectly 

 fixed, the middle point will sustain - of the whole pressure. 



Let the half length be a, the distance of any point from the 

 middle .r, and the pressure on the end // ; then the strain at 

 the point, being the joint result of all the forces acting on either 

 side of it, as on the arm of a lever of which it is the fulcrum, 



will be y{a—x) — {a—x)^{a~x)^ since the weight of the 

 portion a-~x acts at the distance -^ (a— x); and the curvature 



will 



1 t 



