Lexicon medicum; or medical dictionary; containing an explanation and comparative, botany, chemistry, materia medica, midwifery, pharmacy, physiology, practice of physic, surgery, and the various branches of natural philosopy, connected with medicine / Selected, arranged and compiled, from the best authors, by Robert Hooper.

  • Robert Hooper
Date:
1839
Catalogue details

Licence: Public Domain Mark

Credit: Lexicon medicum; or medical dictionary; containing an explanation and comparative, botany, chemistry, materia medica, midwifery, pharmacy, physiology, practice of physic, surgery, and the various branches of natural philosopy, connected with medicine / Selected, arranged and compiled, from the best authors, by Robert Hooper. Source: Wellcome Collection.

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    in tlie same animal at different ages ; it is white I and insipid in young subjects, and has a deeper colour and stronger taste in those more ad¬ vanced in life. The i'at is always solid in the dead body ; but Winslow, Haller, and many other writers, have represented it as fluid during life : this opinion, however, may be easily dis¬ proved by examining the substance in question during the progress of surgical operations, when it presents itself as a soft and easily compressible solid. The chemical properties of this import¬ ant animal product have been fully investigated by M. Chevreuil ; the following account of his ! discoveries, originally published in the Annales de Chimie, is abbreviated from Dr. Ure’s Che- ( mical Dictionary. By dissolving fat in a large quantity of alko- ! hoi, and observing the manner in which its j different portions were acted upon by this i substance, and again separated from it, it is I concluded that fat is composed of an oily sub¬ stance, which remains fluid at the ordinary tem- j perature of the atmosphere; and of another fatty substance which is much less fusible. Hence it follows, that fat is not to be regarded j as a simple principle, but as a combination of the above two principles, which may be separated without alteration. One of these substances j melts at about 45°, the other at 100° ; the same j quantity of alkohol which dissolves 3-2 parts of the oily substance, dissolves 1 -8 only of the fatty substance : the first is separated from the al¬ kohol in the form of an oil ; the second in that i of small silky needles. Each of the constituents of natural fat was then saponified by the addition of potash ; and an accurate description given of the compounds which were formed, and of the proportions of their constituents. The oily substance became saponified more readily than the fatty substance; the residual fluids in both cases contained the sweet oily principle ; but the quantity that pro¬ ceeded from the soap formed of the oily sub¬ stance was four or five times as much as that from the fatty substance. The latter soap was found to contain a much greater proportion of the pearly matter than the former, in the pro¬ portion of 7-5 to 2 9 ; the proportion of the fluid fat was the reverse, a greater quantity of this being found in the soap formed from the oily substance of the fat. When the principles which constitute fat unite with potassa, it is probable that they ex¬ perience a change in the proportion of their elements. This change developes at least three bodies, margarine, fluid fat, and the sweet prin¬ ciple ; and it is remarkable that it takes place without the absorption of any foreign substance, or the disengagement of any of the elements which are separated from each other. As this change is effected by the intervention of the alkali, we may conclude that the newly formed principles must have a strong affinity for salifi¬ able bases, and will, in many respects, resemble the acids ; and, in fact, they exhibit the leading characters of acids, in reddening litmus, in decomposing the alkaline carbonates to unite with their bases, and in neutralising the specific properties of the alkalis. Having already pointed out the analogy be¬ tween the properties of acids and the principles into which fat is converted by means of the alkalis, the next object was to examine the action which other bases have upon fat, and to observe the effect of water, and of the cohesive force of the bases upon the process of saponific¬ ation. The substances which the author sub¬ jected to experiment were soda, the four alkaline earths, alumina, and the oxides of zinc, copper, and lead. After giving a detail of the processes which he employed with these substances respect¬ ively, he draws the following general conclus¬ ions:— Soda, barytes, strontian, lime, the oxide of zinc, and the protoxide of lead, convert fat into margarine, fluid fat, the sweet principle, the yellow colouring principle, and the odorous prin¬ ciple, precisely in the same manner as potassa. I Whatever be the base that has been employed, I the products of saponification always exist in the j same relative proportion. As the above-men- I tioned bases form, with margarine, and the fluid fat, compounds which are insoluble in water, it I follows, that the action of this liquid, as a solv- i ent of soap, is not essential to the process of j saponification. It is remarkable that the oxides of zinc and of lead, which are insoluble in I water, and which produce compounds equally » insoluble, should give the same results with potash and soda—a circumstance which proves ii that those oxides have a strong alkaline power. •: Although the analogy of magnesia to the alka¬ lis is, in other respects, so striking, yet we find that it cannot convert fat into soap under the j same circumstances with the oxides of zinc and t| lead. It was found that 100 parts of hog’s lard rj were reduced to the completely saponified state cl by 16'36 parts of potassa. The properties of spermaceti were next ex- l] amined : it melts at about 112°; it is not much ■1 altered by distillation ; it dissolves readily in hot alkohol, but separates as the fluid cools; ll the solution has no effect in changing the colour jil of the tincture of litmus, — a circumstance, as it 11 is observed, in which it differs from margarine, i a substance which, in many respects, it resembles, fl Spermaceti is capable of being saponified by pi potash, with nearly the same phenomena as jl when we submit hog’s lard to the action of |l potash, although the operation is effected with ik more difficulty. The author’s general conclusion respecting ik the fatty matter of dead bodies is that, even n after the lactic acid, the lactates, and other in- I gredients which are less essential, are removed ill from it, it is not a simple, ammoniacal soap, but < I a combination of various fatty substances with Ip ammonia, potash, and lime. The fatty sub- ! i stances which were separated from alkohol, had Ik different melting points, and different sensible ii properties. It follows, from Chevreuil’s expe- Ik riments, that the substance which is the least |m fusible has more affinity for bases than those IR which are more so. It is observed, that adipo- ip cere possesses the characters of a saponified fat; it it is soluble in boiling alkohol in all propor- If1 tions, reddens litmus, and unites readily with r potash, not only without losing its weight, but l|: