320 
INFLUENCE OF ROSIN ON FATTY SUBSTANCES. 
passes through different degrees of viscidity, like oils of dif- 
ferent qualities, until at 76 degrees it becomes a dense semi- 
fluid. It is an unexpected result, that the addition of one 
part in four of rosin, whose melting point is near 300 degrees 
to lard, whose melting point is at 97 degrees, should render 
it more fluid, reducing its melting point to 90 degrees, im- 
parting to it the properties of a semi-fluid, at a temperature 
as low as 76 degrees, ? and even rendering the preparation of 
a softer consistency than lard itself, at a temperature as low 
as 60 degrees. This compound of lard and rosin has, there- 
fore, two somewhat remarkable properties : — 
1. It prevents in the lard, and probably in all the animal 
oils and fats, their tendency to generate an acid, and thus to 
undergo spontaneous decomposition. A much smaller pro- 
portion of rosin than one-fourth, gives to lard this property, 
destroying, as it does, the tendency of these substances to 
oxidation. Several important practical applications result 
from this property. Its use for lubricating surfaces of brass 
or copper has already been adverted to. It is equally appli- 
cable to surfaces of sheet iron. I have found .a very thin 
coating, applied with a brush, sufficient to preserve Russia 
iron stoves and grates from rusting during summer, even in 
damp situations. I usually add to it a portion of black lead, 
and this preparation, when applied with a brush, in the thin- 
nest possible film, will be found a complete protection to sheet 
iron stoves and pipes. The same property renders the com- 
pound of lard and rosin a valuable ingredient in the compo- 
sition of shaving soap. The quality of shaving soap is greatly 
improved by a larger proportion of oil than is usually em- 
ployed, so as completely to saturate the alkali ; but such soap 
easily becomes rancid when wet with water, and suffered 
to remain damp, as it commonly is when in use. If a cer- 
tain proportion of this compound is added to common Wind- 
sor soap, (say one-half its weight) the tendency to grow 
rancid is prevented. A very soft and agreeable shaving 
compound, or " cream," may be made by steaming in a close 
