Our own observations have shown that heating soils to dryness at a temperature of 110 deg C. greatly increases the freedom with which plant food may be recovered from them by the solvent power of water, and the same heating doubtless improves the physical and biological conditions of the soil as well.  Nitrogen combined as ammonia, and phosphorus, potash and lime are all carried with the smoke or soot, mechanically in the draft and arrested upon the inner walls of the kangs or filter into the porous brick with the smoke, and thus add plant food directly to the soil.  Soot from wood has been found to contain, as an average, 1.36 per cent of nitrogen; .51 per cent of phosphorus and 5.34 per cent of potassium.  We practice burning straw and corn stalks in enormous quantities, to get them easily out of the way, thus scattering on the winds valuable plant food, thoughtlessly and lazily wasting where these people laboriously and religiously save.  These are gains in addition to those which result from the formation of nitrates, soluble potash and other plant foods through fermentation.  We saw many instances where these discarded brick were being used, both in Shantung and Chihli provinces, and it was common in walking through the streets of country villages to see piles of them, evidently recently removed.

The fuel grown on the farms consists of the stems of all agricultural crops which are to any extent woody, unless they can be put to some better use.  Rice straw, cotton stems pulled by the roots after the seed has been gathered, the stems of windsor beans, those of rape and the millets, all pulled by the roots, and many other kinds, are brought to the market tied in bundles in the manner seen in Figs. 74, 75 and 76.  These fuels are used for domestic purposes and for the burning of lime, brick, roofing tile and earthenware as well as in the manufacture of oil, tea, bean-curd and many other processes.  In the home, when the meals are cooked with these light bulky fuels, it is the duty of some one, often one of the children, to sit on the floor and feed the fire with one hand while with the other a bellows is worked to secure sufficient draft.  The manufacture of cotton seed oil and cotton seed cake is one of the common family industries in China, and in one of these homes we saw rice hulls and rice straw being used as fuel.  In the large low, one-story, tile-roofed building serving as store, warehouse, factory and dwelling, a family of four generations were at work, the grandfather supervising in the mill and the grandmother leading in the home and store where the cotton seed oil was being. retailed for 22 cents per pound and the cotton seed cake at 33 cents, gold, per hundredweight.  Back of the store and living rooms, in the mill compartment, three blindfolded water buffalo, each working a granite mill, were crushing and grinding the cotton seed.  Three other buffalo, for relay service, were lying at rest or eating, awaiting their turn at the ten-hour