THE CHEMISTRY OF COOKERY. 101 



ized nearly to blackness, and all their powers of offensiveness vanish, 

 as such offense is due to slow decomposition of the original organic 

 compounds, which now exist no longer, and the remaining caramel or 

 carbon cinders being quite inoffensive or no further decomposable by 

 atmospheric agency. 



In the more violent factory process of purification by sulphuric 

 acid the similar action which occurs is due to the powerful affinity of 

 this acid for water ; this may be strikingly shown by adding to thick 

 sirup or pounded sugar about its own bulk of oil of vitriol, when a 

 marvelous commotion occurs, and a magnified black cinder is pro- 

 duced by the separation of the water from the sugar. 



The following simple practical formula may be reduced from these 

 data. When a considerable quantity of much-used frying fat is accu- 

 mulated, heat it to about 300 Fahr., as indicated by the crackling of 

 water when sprinkled on it, or, better still, by a properly constructed 

 kitchen thermometer graduated to about 400 Fahr. Then pour the 

 melted fat on hot water. This must be done carefully, as a large 

 quantity of fat at 400 poured upon a small quantity of boiling water 

 will illustrate the fact that water when suddenly heated is an explo- 

 sive compound. The quantity of water should exceed that of the fat, 

 and the pouring be done gradually. Then agitate the fat and water 

 together, and, if the operator is sufficiently skillful and intelligent, the 

 purification may be carried further by carefully boiling the water 

 under the fat, and allowing its steam to pass through ; but this is a 

 little dangerous, on account of the possibility of what the practical 

 chemist calls " bumping," or the sudden formation of a big bubble of 

 steam that would kick a good deal of the superabundant fat into the 

 fire. 



Whether this supplementary boiling is carried out or not, the fat 

 and the water should be left together to cool gradually, when a dark 

 layer of carbonized impurities will be found resting on the surface of 

 the water, and adhering to the bottom of the cake of fat. This may 

 be peeled off and put into the waste grease-pot, to be further refined 

 with the next operatiou. Ultimately the worst of it will sink to the 

 bottom of the water. Then it is of no further value, and will be found 

 to be a mere cinder. 



XVII. 



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Regarding the fat used in frying as a medium for conveying heat, 

 freedom from any special flavor of its own is a primary desideratum. 

 01ive-o;l of the best quality is almost absolutely tasteless, and, having 

 as high a boiling-point as animal fats, it is the best of all frying media. 

 In this country there is a prejudice against the use of such oil. I have 

 noticed at some of those humble but most useful establishments where 

 poor people are supplied with penny or twopenny portions of good fish, 

 better cooked than in the majority of " eligible villa residences," that 



