Comparative Analysis of the Gum Resins. 353 
7. The decoction of’ gall-nuts forms a precipitate in the 
solution of the guin of frankincense, which is not the case 
with that of myrrh. | tye 
8. Lime-water in excess does not affect its transparency 
even after a length of time. 97 m. 7 
'g. This gum is carbonized by the sulphuric acid, but 
without giving out acetous vapours on heating the mixture: 
hat substance is it therefore that neutralizes the lime in 
this’ gum? I once’ suspected that it was benZoic acid; but 
this opinion requirestonfirmation. 
“Qo. The gum! of frankincense heated with nitric acid 
deposits, particularly on cooling, a large quantity of a very 
white crystalline-like ‘powder : ‘on continuing the evapora- 
tion’ to dryness, we obtained a residue, which, after being 
well washed’ and’ dried, furnished the sacco-lactic acid of 
Scheele, (the mucous acid Of Fourcroy,) forming one-third 
in weight of ‘the guin em] layed’ in the experiment: the 
water of the washitigs Cdutained oxalic and malic acid, but 
in’a’small quantity! “NS ee Kyi 
This action of the nifric acid on the gum of frankincense 
shows that it differs from gum arabic, which does not afford 
mines acid hs A) hs Oh Pl bie 
D. The liquor produced from the 25 grammes of incense 
treated by alcohol A, when evaporated to dryness, afforded 
14 grammes of resin; whence it results that there is a loss 
of two grammes, which I ascribe in a great measure to the » 
volatile oil. 
1. The resin of the incense is of a reddish-yellow colour, 
becomes very brittle upon cooling, bas no perceptible 
taste, becomes idio-electrical, and resembles pitch-resin. 
2. It softens in boiling water; but it requires a greater 
degree of heat to melt it. When exposed to a flame it~ 
burns, sending out a smell which is not disagreeable. 
3. This resin when heated to dryness with a solution of 
caustic potash left a residue not very soluble, which, after 
having been well washed, is dilutable in boiling water, pro- 
ducing an emulsive liquid more or less thick. The resin. 
of pitch unites with the alkalis with much more pa 
4, Uo 
thinks, on the contrary, that it is owing toa decomposition of the nitric 
acid and of the metallic oxide: but the examination of these sediments con- 
_stantly presented to me a combination of gum and metallic oxide. 
Gum arabic is also abundantly precipitated from its soluvions by the sub- 
acetate of lead: it isthe samecase with gum adracanth, ‘Ihese sediments 
resemble cheese : if we burma them, they leave lead in the metallfc state. 
* Resinous substances havenot been as yet examined with the minuteness 
and attention which they deserved, as may be eavily proved, ftora the iw 
Vol. 37. No, 157. Mgy 1811. . 
