6 BULLETIN 898, U. S. DEPARTMENT OF AGRICULTURE. 
These attack the tin or iron of a can or tank in which the turpentine 
may be stored, and the dissolved iron helps to darken the color. For 
this reason turpentine should not be stored in partially filled iron or 
tin cans or tanks unless they have: first been painted inside with 
a turpentine-resisting paint. 
The absorption of oxygen begins as soon as the gum exudes from s 
the tree. ‘Thus when the face is quite long, with a correspondingly 
longer exposure of the gum to light and air, the yield of turpentine 
is lowered, the odor grows less fragrant, and the gum becomes more 
viscous. The heavy, oily, almost resinous nature of the oxidation 
products, which have high boilmg points, accounts in part for the 
increased tendency to froth during distillation of old high-box gum, 
and causes the turpentine obtamed during the latter part of the 
distillation of such gum to be usually heavy and discolored, and the 
rosin to be decidedly darkened, due to the higher temperature which 
must be maintained in order to abstract all the turpentine. 
Spirits of turpentine is believed to owe its superiority as a ace 
thinner to its property of absorbing oxygen from the air, the drying 
of paint being due to the absorption of oxygen from the air by the 
linseed or other drying oil, forming a hard insoluble film of lmoxyn. 
It is said that turpentine acts as an oxygen carrier, transferring 
oxygen from the air to the linseed oil, and finally adding to the paint 
film the nonvolatile residue left after evaporation, which also acts 
like a drying oil. 
Treating turpentine with small quantities of ordinary concentrated 
sulphuric acid forms a new hydrocarbon called terpinene with a 
boiling point of 180° C. Heating turpentine with larger quantities 
of concentrated sulphuric acid or with fuming sulphuric acid chars 
or carbonizes it, with the formation of small amounts of resinous 
matter. This action is the basis of several methods for detecting 
the presence of adulterants in turpentine. Strong nitric acid com- 
bines with turpentine with great energy, the latter being ignited un- 
less kept cold. The product of such action is a brown, resinous, 
gummy mass. On the other hand, dilute nitric or sulphuric acid 
brings about a gradual conversion of the pinene in turpentine to 
terpene hydrate and dipentene. 
On passing dry hydrogen chlorid (hydrochloric acid gas) into tur- 
pentine which is kept cold by immersing the container in a mixture 
of salt and ice, a combination of the two takes place, forming what 
is known as pinene hydrochlorid. This is a crystalline white body 
having an odor much like that of camphor, and is called artificial 
camphor. It is quite volatile at ordinary temperatures, evaporating 
completely when exposed to the air. 
In the manufacture of synthetic camphor, which is being carried 
on at present on a commercial scale, the preparation of pinene 
