CHAPTER X.

FAT—MILK.

WE all know that there is a considerable difference between raw fat and cooked fat; but what is the _rationale_ of this difference? Is it anything beyond the obvious fusion or semi-fusion of the solid?

These are very natural and simple questions, but in no work on chemistry or technology can I find any answer to them, or even any attempt at an answer. I will therefore do the best I can towards solving the problem in my own way.

All the cookable and eatable fats fall into the class of ‘fixed oils,’ so named by chemists to distinguish them from the ‘volatile oils,’ otherwise described as ‘essential oils.’ The distinction between these two classes is simple enough. The volatile oils (mostly of vegetable origin) may be distilled or simply evaporated away like water or alcohol, and leave no residue. The fixed oils similarly treated are dissociated more or less completely. This has been already explained in