CHEMICAL SCIENCE. 237 



be added in fine powder, and the mixture well stirred (without the 

 application of heat), it softens and so nearly approaches a lluid as to 

 run freely when taken up on the stirring-rod, at a temperature of 72. 

 On melting- the mixture, and setting it aside to cool, the following 

 changes take place : At 90 it remains transparent and limpid ; at 

 87, a pellicle begins to form on the surface, and soon after it be- 

 gins to grow slightly viscid, and as the temperature descends, it passes 

 through different degrees of viscidity, like oils of different qualities, 

 until, at 76, it becomes a dense semi-fluid. It is an unexpected re- 

 sult, that the addition of one part in four of rosin, whose melting point 

 is near 300, to lard, whose melting point is at 97, should render it 

 more fluid, reducing its melting point to 90, imparting to it the prop- 

 erties of a semi-fluid, at a temperature as low as 76, and even render- 

 ing the preparation of a softer consistency than lard itself, at a 

 temperature as low as 60. This compound of lard and rosin has, 

 therefore, two somewhat remarkable properties : 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 proportion 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 al- 

 ready been adverted to. It is equally applicable to surfaces of sheet- 

 iron. I have found a very thin coating, applied with a brush, suffi- 

 cient 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 

 thinnest possible film, will be found a complete protection to sheet- 

 iron stoves and pipes. The same property renders the compound of 

 lard and rosin a valuable ingredient in the composition of shaving- 

 soap. The quality of shaving-soap is greatly improved by a larger 

 proportion of oil than is usually employed, 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 

 certain proportion of this compound is added to common Windsor 

 soap (say one half its weight), the tendency to grow rancid is pre- 

 vented. A very soft and agreeable shaving compound, or ' cream,' 

 may be made by steaming in a close cup a cake of any common shav- 

 ing-soap, so as to reduce it to a soft consistency, and then mixing in- 

 timately with it half its weight of our resinous preparation, adding a 

 few drops of some odoriferous substance. The same compound forms 

 an excellent water-proof paste for leather. Boots, when treated with 

 it, will soon afterwards take the usual polish when blacked, and the 

 soles may be saturated with it without danger of soiling the floor, as 

 it does not rub off, while the leather is rendered, in a high degree, 



ji _ . 



impervious to water. The perfect solution into which rosin passes 

 when heated with oil suggested the possibility of improving, in this 

 way, the quality of oils used for illumination, and, by its reducing the 

 melting point of lard, to render that more suitable for burning in solar 

 lamps. I therefore added powdered rosin to lard oil, in the proper- 



