354 Comparative Analysis of the Gum Resins. 
4. Cold sulphuric acid, the resin of incense, and water pro- 
duce a white sediment in this solution, which is of a red 
colour. If we heat it for some time, the water then sepa- 
rates from it a black resin soluble in the nitric acid, which 
converts it by evaporation into a brown residue of an astrin- 
gent bitter taste, and the solution of which in water preci- 
pitates gelatine, but not, sulphate of iron, 
5. The resin of incense when heated to dryness with 
eight times its weight of nitric acid at 382, is converted al- 
most entirely into the resipiform matter, the properties of 
which | have already described, The washings which did 
not contain, oxalic, acid furnished. by evaporation a resi- 
due, which when again heated with nitric acid did not give 
the tannin substance, discovered by Mr. Hatchett, but a bit- 
ter soluble substange,. which was partly precipitated upon 
cooling fromn,its solution, in boiling water, soluble also in 
alcohol,: and. producing. precipitates in several metallic so- 
eae 
Jutions.4 ont eon idouord- et) dod J 
This substance seems to;me to have properties analogous 
f 
QO 
and frequently inaccurate! observations: which have ‘been made as to the 
chemical properties of these budies. Thus, it .has been generally supposed 
that the alkalis exercise no action on the resins, In order to verify this as- 
sertion, | made the following experiments on the resins: nie 
To a very Weak’ Solutiin of potash, cold 1 added gradually some pitch- 
resin ip powder there -resultedya perfect saponaceous, solution, which be- 
came thick and thready like the white of an egg. ‘lhe weakest acids pro- 
duce very abundant white sediments: it is the Same with the alkalis and the 
neutral salts, on aceount of their greater affinity for water than that of the 
resinous soaps. -/A large quantity, of common water also decomposes this 
soap; the sediment which isthe resultis only partly soluble im alcohol: 
that part which cannot be dissolved still contains plenty of resin united to lime. 
If we pour muriate’ of lime into ‘the: sdlutidn of this resinous ‘soap, the 
‘mixture goes/into a whitish massresembling:/ broth, and formed of resin and 
ime. Foy og ret ote + ¢ T Mv ew J 
All the metallic solutions decompose in toto the soap of pitch-resin. The 
sediments which are produced migh¢ iti many eases be employed in painting. 
Fifty grammies/jof> pitch-resin; heated: wntil) saturation with solution of 
potash were/entirely dissolved: we obtained by evaporation 69 grammes of 
solid resinous soap, dry at a cold température, Of a brown colour, and which 
1 found to be perfectly similar to Starkey’s soap. Messrs. Baumé and Le- 
gendre had therefore gaod reason torjthink that it is only the thick and re- 
sinous part of the essence of turpentine which can be really combined with 
‘potash: for this alkali acis upon volatile oil, only by favouring its cgn- 
version into resin in order to unite with it afterwards. 
The volatile alkali greatly diluted in Water, also unites with pitch-resin 
avith great facility, and speedily converts it to the soapy state. This com- 
jbination aliluted with water acquires through time the consistence of tar. 
lought not to omit to mention, that the svap made from potash and the 
above resin might'be used instead of common soap for domestic purposes. 
‘At produces abundance of froth, and whitens well: only it gives a slight re- 
sinous smell to nen, which is dissipated, however, on exposure to the air. 
‘The economy and facility with which ic might be manufactured would 
doubtless enhance its properties, 
with 
