IV. PUT THE STOCK-POT ON A GENTLE FIRE, so that it may heat gradually. The albumen will first dissolve, afterwards coagulate; and as it is in this state lighter than the liquid, it will rise to the surface; bringing with it all its impurities. It is this which makes _the scum_. The rising of the hardened albumen has the same effect in clarifying stock as the white of eggs; and, as a rule, it may be said that the more scum there is, the clearer will be the stock. Always take care that the fire is very regular.
V. REMOVE THE SCUM when it rises thickly, and do not let the stock boil, because then one portion of the scum will be dissolved, and the other go to the bottom of the pot; thus rendering it very difficult to obtain a clear broth. If the fire is regular, it will not be necessary to add cold water in order to make the scum rise; but if the fire is too large at first, it will then be necessary to do so.
VI. WHEN THE STOCK IS WELL SKIMMED, and begins to boil, put in salt and vegetables, which may be two or three carrots, two turnips, one parsnip, a bunch of leeks and celery tied together. You can add, according to taste, a piece of cabbage, two or three cloves stuck in an onion, and a tomato. The latter gives a very agreeable flavour to the stock. If fried onion be added, it ought, according to the advice of a famous French _chef_, to be tied in a little bag: without this precaution, the colour of the stock is liable to be clouded.
VII. BY THIS TIME we will now suppose that you have chopped the bones which were separated from the meat, and those which were left from the roast meat of the day before. Remember, as was before pointed out, that the more these are broken, the more gelatine you will have. The best way to break them up is to pound them roughly in an iron mortar, adding, from time to time, a little water, to prevent them getting heated. It is a great saving thus to make use of the bones of meat, which, in too many English families, we fear, are entirely wasted; for it is certain, as previously stated (No. 102), that two ounces of bone contain as much gelatine (which is the nutritive portion of stock) as one pound of meat. In their broken state tie them up in a bag, and put them in the stock-pot; adding the gristly parts of cold meat, and trimmings, which can be used for no other purpose. If, to make up the weight, you have received from the butcher a piece of mutton or veal, broil it slightly over a clear fire before putting it in the stock-pot, and be very careful that it does not contract the least taste of being smoked or burnt.