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ISAROL

A substitute for ichthyol used as an irritant in skin affections. ISATIN A synthetic reddishyellow crystalline substance, fairly soluble in hot water, ether, and alcohol, which can be prepared by the oxidation of indigo with nitric acid and is convertible into aniline by the action of potash. Its melting point is 200 degrees C., and it is used in dyeing.

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INVERTASE

An enzyme present in ordinary yeast which, apart from the yeast cells themselves, has the power of converting cane sugar into glucose and fructose by hydrolysis, to the reported extent of 200,000 times its own weight of cane sugar without then losing its eifect The product is known as “invert sugar,” and whereas a solution of cane sugar is dextrorotatory, the hydrolyzed product is lsevorotatory, the fructose being more strongly laevo rotatory than the glucose is dextrorotatory.

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ICELAND SPAR

CalciteTransyaient Calcspar}A mineral form of calcium carbonate.

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INTERMEDIATES

A general term for a great number of complex derivatives obtained by chemical processes from anthracene, benzene, cresols, naphthalene, phenol, toluene, and other direct coaltar products, all of which are used in the manufacture of synthetic dyes. They include aniline oil, naphthol, naphthalene, naphthylamines, phthalic anhydride, anthran ilic acid, dmethylaniline, nitrobenzene, paranitraniline, resoicin, salicylic acid, and many other compounds, some of which are described under theii respective names.

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INDAMINES

A group of aniline dyes including “phenol blue” 2N.CeH4.N:C4H4i0.

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INULIN or ALANT STARCH

xA carbohydrate contained in dahlia bulbs to the extent of about 10 per cent, of the weight of the ripe tubers, and in smaller proportions in the roots of other members of the Composite, such as chicory and artichokes. In the pure state it is a white powder resembling starch, but, unlike that substance, it dissolves in aqueous sodium hydroxide and in hot water to a clear solution, and is not coloured blue by iodine. It is unaffected by diastase, and is not fermentable by yeast, but when boiled with water or dilute acid it is converted into a variety of fructose. It is used in the preparation of diabetic bread, and is a strongei sweetener than cane sugar.

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ICELAND MOSS

A lichen containing a mucilage which can be extracted by hot water.

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ISOTOPES

A term introduced to explain the apparent existence of very nearly allied but nonseparable forms of chemical elements, the general chemical properties being identical, but exhibiting variation in their atomic weights, or mass, or molecular arrangement. Thus it is supposed that magnesium, silicon, and chlorine, in addition to neon, are mixtures of isotopes; further, that nickel, copper, zinc, mercury, and other of the elements, are really mixtures of isotopes. Ionium and thorium are said to be isotopes. Many of the conclusions of the investigators of these matters are based upon radioactive evidence, and others upon the separation of gases by diffusion, but much remains to be done before the subject and the electron constitution or matter can be regarded as satisfactorily established.

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INDIAN RED

A natural pigment from the Persian Gulf, containing ferric silicate.

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IODINE VALUE

.This determination, as commonly performed on samples of oils, fats, and waxes, is used to indicate the degree of unsaturation of the compound that is, the number of pairs of carbon atoms in which two valency bonds are concentrated between the two carbon atoms. Any such double linkage is in a state of strain, and when the substance containing it comes in contact with certain other substances, one of the bonds breaks and two atoms of the new substance are attached, one to each of the carbon atoms originally joined by the double linkage. Thus every two atoms of the reagent absorbed represent one double linkage in the original substance. The reagent used in the Hubl or Wij method is iodine monochloride, which adds on one atom of iodine to the one carbon atom, and one atom of chlorine to the other. Thus in this case, one atom of iodine absorbed indicates the presence of one double linkage. The method of Hubl is to make up an iodine monochloride solution from iodine and mercuric chloride, and add excess of this to a known weight of the substance. After standing for some lime, the excess of iodine chloride is estimated by the potassium iodide and thiosulphate method: a blank test is carried out alongside, using an equal quantity of the reagent without the substance, and the difference indicates the amount of iodine absorbed by the substance. The iodine value may be defined as the amount of iodine chloride absorbed by 100 grms. of the substance, expressed in terms of iodine. The drying properties of oils are in almost direct ratio of their iodine values. Saturated substances such as the paraffins have iodine value nil.

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