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FRANKINCENSE.

An oleoresinous exudation from the spruce fir, from which burgundy pitch is made by melting and straining it through a cloth.

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FELSPARS

Compound mineral silicates of aluminium and other metals found abundantly in nature. There are many deposits in Cornwall, Ireland, Wales, and Scotland, as much as 14 per cent, potassium oxide being found in some small veins of orthnclase, or potaJifdspar, although most of them are not suitable for potash extraction.

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FOODS

are the other substances which, in addition to water and air, serve to repair the various tissues of the body and to renew its energy. They are generally classified under the headings of proteins, carbohydrates, and fats, although vegetable acids and mineral salts are essential to a perfect dietary, as also a small quantity of the mysterious substances called hormones and vitamines. Tea, coffee, and alcohol are often regarded as mere stimulants or accessories, but while tea and coffee may be so viewed, alcohol is a real food when taken in moderation, all of it being consumed in the body and serving to replace so much other food. It is usual nowadays to calculate food values in terms of calories Cheat units, a kilccalorie being the quantity of heat sufficient to raise a kilogramme of water one degree Centigrade, and it is reckoned that proteins and carbohydrates each produce 4i calories for every gramme consumed as against 93 calories for each gramme of fat consumed. A committee of the Royal Society reported during the recent war that each man engaged in active work requires per day 100 rms. or 3 ozs. protein, 100 grms. or 31 ozs. fat, and 500 grms. or 17J ozs. carbohydrates, totalling approximately 3,400 calories per man per day. In this connection it should be remembered that fats and carbohydrates are 10 some extent interchangeable and both are similarly interchangeable with alcohol to some degree. Taking the five prewar years the following table gives the quantities in metric tons of the total foods imported and Some produced:

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FULMINATING GOLD

A compound of auric oxide 3 and ammonia, of explosive character, the exact chemical constitution of which has not been ascertained.

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FRACTIONAL DISTILLATION

affords the means of separating, more or less, theseveral constituents of mixed distillable liquids, by collecting the portions or fractions which pass over at varying temperatures. For example, alcohol boils at 78 degrees C. and aniline at 185 degrees C., so that a mixture of the two substances can be separated by this process.

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FORMULAE

The arrangement of symbols representing the chemical composition of substances. The symbols which are used are explained in the several sections dealing with Chemical Compounds,Chemical Interactions, and Elements, and the formulae employed are of various types. The ordinary formulae indicate the molecular composition without respect to any particular molecular arrangement or structure thus NaCl expresses the combination of 1 atom of sodium with 1 atom of chlorine in 1 molecule of salt. Again, the formula 2S04 expresses the combination of 2 of the groups NH4 with 1 of S04 in 1 molecule of ammonium sulphate, and so fortn. The empirical formula of a substance is ascertained from the results of its analysis, the percentages of elements found present being divided by their atomic weights. For example, hydrocyanic acid upon analysis is shown to contain as follows: and if these percentages are div ided by the atomic weights of the three elementsviz., II = x, C=i2, and N=i4it will be found that the quotients are practically identical, so that the component elements are combined in the proportions of one eachviz., HCN, which is the simplest formula of the substance. Or again, taking salt, it yields upon analysis 39316 per cent, sodium and 6o6?>4 per cent, chlorine, and the division of these numbers by the atomic weights 23 and 355 shows the two components to be contained in the elemental proportions so that the empirical formula is NaCl. Constitutional or Rational formulae, on the other hand, are used to express a sense of construction or structure, as when, for example, ammonium cyanate is resolved by heating into urea, the change may be expressed as follows: CNO = CO2 in order to show that, although empirically the composition of the two substances is the same, being concretely expressed by the formula CN2H40, the molecular arrangements or structures are different. Again, the empirical formula of ethyl alcohol is C2H#0, but when expressed constitutionally as C2H6, it is seen that the molecule has an alcoholic structure and that the group HO can be replaced or substituted by other groups. So again, acetic acid 2 may be expressed constitutionally in several ways, thus:

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FIRE DAMP

An explosive gas naturally produced in coalmines, and chiefly composed of methane admixed with air, nitrogen, and some carbon dioxide.

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FUMARIC ACID

is a natural constituent of some plants and lichens, including Fumaria officinalis, Glauctum flavum, and Iceland moss. It crystallizes in colourless prisms, is inodorous, has an acid taste, and is readily soluble in hot water, alcohol, and ether. It is nearly allied in constitution to malic, acid, and it is resolved into succinic acid by the action of reducing agents.

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FLUORINE

Atomic weight, 19. Fluorine is found in nature combined with calcium in the mineral fluorspar and is a constituent of cryolite a double fluoride ol sodium and aluminium found in Colorado and Greenlandand other minerals. It is also present in small quantities in bones and the enamel of teeth. Fluorine can be obtained in quantity by the electrolysis of fused potassium hydrogen fluoride or of anhydrous hydrofluoric acid at 230 C., and is, at ordinary temperatures, a pale yellowish gas of very active chemical, corrosive, and poisonous qualities, which attacks glass with avidity, bat is insoluble in water. When cooled to a temperature of187 degrees C. it condenses to the liquid state in the form of a mobile yellow fluid with a characteristic odour something like that of chlorine, and at a still lower temperature it assumes tiie solid form and is almost white. Fluorine acts strongly upon all metals, even gold and platinum to some extent, and many of them pass into a state of inflammation when thrown in a finely divided state into the gas. It also attacks organic substances with violence. A combination with hydrogen known as hydrofluoric acid gas is made by warming a mixture of strong sulphuric acid and powdered calcium fluoride in a leaden or platinum vessel: It is very soluble in water, and is largely employed for etching purposes, as, for example, making the graduations on glass measuring apparatus. The object to be marked in this way is coated with melted wax, and after making the design or marks on the coated glass, it is exposed to the action of the acid either in the form of gas or liquid, with the result that the glass is eaten into where exposed by the markings, the fluorine having no action on the wax. For some commercial purposes, an aqueous solution of this acid of 60 per cent, strength is produced. Hydrofluoric acid vapour is irritating and injurious to the respiratory organs, and the liquid produces ulcerated sores on the skin, and is altogether a very dangerous chemical compound. There are fluorides corresponding to the chlorides and also a number of double fluorides. The fluorides of potassium, sodium, and iron are but sparingly soluble in water, while the fluorides of silver and tin are easily soluble. Most of the fluorine compounds are easily fusible, and when ignited in a current of steam many of them are converted into oxides and hydrofluoric acid is evolved.

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FERRICYANIBES

are compound cyanides produced from ferrocyarides by the action of oxidizing agentsfor example, potassium ferrocyanide becomes converted into K62 or 2K3Fe6.

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