Page:Encyclopædia Britannica, Ninth Edition, v. 9.djvu/843

 F U E F U E 807 scion ; but the easiest and most usual method of propaga tion is by cuttings. As one of the most expeditious ways of procuring these, Loudon recommends to put plants in heat in January, and to take their shoots when three inches in length. For summer flowering in England they are best made about the end of August, and should be selected from the shortest-jointed young wood. Coarse brown sand inter mixed with a little leaf-mould, with a surface-layer of silver- sand, affords them a good soil for striking. In from two to three weeks they may be put into 3-inch pots containing a compost of equal parts of rich loam, silver-sand, and leaf- mould. They are subsequently moved from the frame or bed, first to a warm and shady, and then to a more airy part of the greenhouse. In January a little artificial heat may be given, to be gradually increased as the days lengthen. The side-shoots are generally pruned when they have made three or four joints, and for bushy plants the leader is stopped soon after the first potting. Care is taken to keep the plants as near the glass as possible, and shaded from bright sunshine, also to provide them plentifully with water, except at the time of shifting, when the roots should be tolerably dry. For the second potting a suitable soil is a mixture of well-rotted cow-dung or old hotbed mould with leaf mould and sandy peat, and to promote drainage a little peat-moss may be placed immediately over the crocks in the lower part of the pot. Weak liquid manure greatly promotes the- advance of the plants, and should bo regularly supplied twice or thrice a week during the flowering season. After this, water is gradually withheld from them, and they may bo placed in the open air to ripen their wood. The com mon garden fuchsia, F.fulyens, stands the winter in England if cut down and covered with 4-6 inches of dry ashes (Smee), and many other species may be grown in the open air if afforded a little protection from frosts. F. discolor, a native of the Falkland Islands, is a particularly hardy species (see Trans. Hart. Soc. Lond., 2d ser., ii. p. 284). The nectar of fuchsia flowers has been shown by Mr A. S. Wilson (Rep. Brit. Assoc., 1878) to contain nearly 78 per cent, of cano sugar, the remainder being fruit sugar. The berries of some fuchsias are subacid or sweet, and edible. From cer tain species a dye is obtainable. The so-called &quot;native fuchsias &quot; of Southern and Eastern Australia are plants of the genus Correct, and natural order Rutacece. See J. C. London, Arboretum, vol. ii. pp. 942-5 ; Felix Forcher, Histoirc ct Culture du Fuchsia, Paris, 1874 ; F. W. Burbidge, The Propagation and Improvement of Cultivated Plants, 1877 ; The Floral World, 1878, pp. 74-76, 253-4. (F. H. B.) FUEL. This term includes all substances that may be usefully employed for the production of heat by combustion with atmospheric air or oxygen. Any element or combin ation of elements susceptible of oxidation, i.e., any substance electro-positive to oxygen, may under particular conditions be made to burn ; but only those that ignite by a moderate preliminary heating, and burn with comparative rapidity, and, what is practically of equal importance, are obtainable in quantity and at a moderate price, come fairly within the category of fuels. Among elementary substances only hydrogen, sulphur, carbon, silicon, and phosphorus can be so classed, and of these the last two are only of special application. More important than the elements are, how ever, the carbohydrates, or compounds of carbon, hydro gen, and oxygen, which form the bulk of the natural fuels, wood, peat, and coal, as well as of their liquid and gaseous derivatives, coal gas, coal tar, pitch, oil, fcc., which are pos sessed of great fuel value. Carbon in the elementary form has its nearest representatives in charcoal and coke. In the determination of the value of fuel two principal factors arc involved, namely, the calorific power, or the total amount of heat obtainable from the perfect combustion of its constituents, and the calorific intensity, or pyrometric effect which is the temperature attained by the gaseous pro ducts of the combustion. The first of these is constant for any particular composition, and does not vary with the method of combustion, the quantity of heat developed by the combustion of a unit of carbon or hydrogen being the same whether it be burnt with oxygen, air, or a metallic oxide. The calorific intensity, on the other hand, being inversely pro portional to the volume of gases produced, it is obvious that if the combustion is effected with pure oxygen the result ing carbonic acid (in the case of carbon) may be very much hotter than when air is used, as the duty of heating up an additional quantity of nitrogen rather more than three times the weight of the oxygen is in the latter case imposed upon a similar weight of carbon. Theoretically 1 unit of carbon combines with 2 67 units of oxygen to form 3 G7 units of carbonic acid, whose specific heat is 216. The resulting maximum temperature of the gases produced therefore cannot exceed but when a similar weight of carbon is burnt with air, the gases are diluted with 8 88 units of nitrogen, whose speci fic heat is 244. The highest temperature possible in the products of combustion in this case does not exceed 8080 = 07310 c 3-67x0-216 4-8-88x0-24 The calorific value of a fuel may be determined by direct experiment, either by complete combustion on the small scale in a calorimeter, or by practical experiment on a working scale, by ascertaining the effect of a weighed quantity in performing a particular kind of work, such as evaporating water in a steam boiler, the result being ex pressed in the number of pounds of water converted into steam per pound of fuel burnt. It may also be computed from an ultimate chemical analysis, the carbon and so much of the hydrogen as remains disposable for burning, after deducting sufficient to form water with the oxygen present, being credited with the full heating power deriv able from their complete oxidation, according to the results found for these elements by the calorimeter. The pyrometric effect, on the other hand, cannot be either computed or determined experimentally with complete ac curacy, partly because the total combustion of a quantity of fuel in a given time at one operation is practically impossible, but more particularly from the fact that dis sociation of the gaseous compounds produced in burning takes place to a greater or less extent at temperatures far below those indicated as possible by calculation based upon comparisons of the weight of the products of combustion and their specific heat with the calorific value of the sub stance as found by experiment. According to Bunsen, Deville, Dewar, and others who have specially considered this subject, a temperature of about 3000 3 C. will be the maximum attainable from any fuel by any ordinary process of combustion. The calorific powers of the principal ele mentary substances susceptible of use as fuels arc given in the following table ; they are expressed in calories or heat units, signifying the weight of water raised, in temperature 1 C., by the combustion of one unit of the different sub stances, and the corresponding weight of water converted into steam from a temperature of 100 C. Heat Units. Water evapo rated. Burnt to Water, H 8 34,462 62-66 Carbon ,, Carbonic acid, CO., 8,080 14-69 Carbonic oxide, CO 2,474 4-50 Silicon Silicic acid, Si0 7,830 14-24 Phosphorus. . . Sulphur ,, Phosphoric acid, P 5 5 .. ,, Sulphurous acid, SO... 5,747 2,140 10-45 4-09