997 



ISAMIC ACID. 



ISOCHROMATIC LINES. 



Lastly, we quote Professor Buckman's report on the influence of 

 irrigation in modifying or improving the character of natural pasturage. 

 He says : 



"Irrigation, when it can be practised, is though acting indi- 

 rectly the most direct means of getting rid of all extraneous plants 

 from grass herbage, and the most direct encourager of the growth of 

 grass solely that we possess ; in illustration of which we quote the sub- 

 joined table from the ' Journal of the Royal Agricultural Society,' 

 vol. iv., part 2. 



TABLE I. SHOWING THE CHANGE OF HERBS (SOT GRASSES) UNDER IRRIGATION. 



" Here we see a marked decrease in bad plants and a corresponding 

 increase in good to be distinctly traced in two years ; and in four years 

 this decrease is still more rapidly progressing ; and we are enabled to 

 state, aa the result of some seven years' watching, that now the irri- 

 gated meadow presents scarcely a trace of the plants belonging to 

 this table, but all, or nearly all, are replaced by most excellent grasses. 



" The following table represents the changes which took place in 

 twelve species of the meadow-grasses in the same time. This field 

 trebled in value in four years, and U now worth 5/. an acre, its 

 increased value being due not only to the fact of ita growing grass and 

 nothing else, but to ita growing only the best kinds of grasses ; for 

 irrigation acts indirectly by killing weeds and innutritions grasses. 



TAILS II. REPRESENTING THE CHANGES OF GRASSES UNDER IKIUGATION. 



"These tables will at a glance show the practical bearing of irri- 

 gation as an indirect means of getting rid of extraneous meadow plants, 

 and at the same time its direct advantage in encouraging the growth of 



LI Ml -." 



ISAMIC ACID. [ISDIGO.] 



ISAMIDE. [iNDloo.l 



ISATANE. [INDIGO.] 



ISATHYD. [lNDiao.1 



ISATIC ACID. [INDIGO.] 



ISATILIMK. [iNDloo.] 



ISATIM1DE. [INDIGO.] 



I8ATIN. [INDIOO.] 



ISATINIC ACID. [lNDioo.1 



I8ATYDES. [INDIOO.] 



I.SETHIONIC ACID is one of the substances found in the residue 

 from the preparation of ether, but may be formed directly by boiling, 

 for some time, a strong solution of ethionic acid. The formula for 

 ethionic acid is (C,H,,2HO,43O.,) ; not (C.H 4 ,2H0 3 ,4S0 3 ) as repre- 

 sented under ETHIONIC ACID and by ebullition is decomposed into 

 sulphuric and isethionic acids : these may be separated from each 

 other by neutralisation with carbonate of baryta and the isethionate of 

 baryta obtained in tabular crystals by evaporation of the filtered 

 solution. 



Isethionic acid (C t H.,2HO,2SO s ) U uncrystallisable. It is isomeric 

 with sulphovinic acid, but is well characterised by the greater stability 

 of its salt*. The general formula of the itethionatet is (C t H,,HO,MO, 



2SO :1 ) or perhaps (MO,C,H 5 S 2 7 ). They are mostly crystallisable, and 

 when heated with hydrate of potash are decomposed into carbonate, 

 oxalate, sulphate and sulphite of the base, hydrogen being evolved. 



ISINGLASS is animal jelly, or gelatin, nearly pure. The best 

 isinglass is prepared in Russia from the membranes of the sturgeon, 

 especially from its air-bladder and sounds, which are remarkably large. 

 These, when removed from the fish, are washed with cold water, and 

 exposed a little to the air, in order that they may stiffen ; the outer 

 skin is then taken off and rejected, and the remainder cut out, and 

 loosely twisted into rolls, according to the intended size of the pieces, 

 which are called staples, and are known in commerce by the names of 

 long and short staple, and of these the first is the best : these are dried 

 in the air. The best sort of isinglass is used for the table and in 

 confectionary ; it is also largely employed in refining wine and beer. 



Isinglass is nearly colourless, has but little taste or smell, is trans- 

 lucent in thin pieces, and is soluble in water. One part of it dissolved 

 in 100 parts of hot water gives a solution which completely stiffens in 

 cooling. 



Isinglass is also dissolved by most acids readily, and also in solution 

 of potash and soda, but not in alcohol. Several metallic salts and 

 oxides have the property of precipitating a solution of isinglass, but 

 corrosive sublimate does not produce this effect, which serves to 

 distinguish.it from albumen ; but it resembles that substance in being 

 precipitated by infusion of galls or of oak-bark. Isinglass is extremely 

 nutritious. 



The degree in which we are dependent on different countries for our 

 supply of isinglass will be seen by the following figures, which refer to 

 the importations for 1856, presenting a fair average for recent years : 

 From Russia, 525 cwts. ; Brazil, 440 ; East Indies, 233 ; Prussia, 166 ; 

 Guiana, 87; other, countries, 170; equal in the whole to about 

 180,000 Ibs. 



ISIS, one of the chief deities of the Egyptians, the sister and wife 

 of Osiris. Isis was the Goddess of the Earth ; the Universal Mother ; 

 the Goddess of Fecundity, and the cow was therefore sacred to her. 

 In the later dynasties she was the divinity of the moon, Osiris being 

 that of the sun. By the Greeks she was identified with Demeter, and 

 her worship became widely spread through Greece, and subsequently 

 in Rome. She was said to have first taught men the art of cultivating 

 com, whence corn was always carried iu processions at her festivals. 

 The annual festival of Isis in Egypt lasted eight days, during which a 

 general purification took place. The priests of Isis were bound to 

 observe perpetual chastity, their heads were shaved, and they went 

 barefooted. The goddess was often represented as a woman with the 

 horns of a cow. She also appears with the lotus on her head and the 

 sistrum in her hand ; and her head in some instances is seen covered 

 with a hood. Heads of Isis are a frequent ornament of Egyptian 

 capitals on the pillars of the temples, as in the facade of the temple of 

 Denderah, and the column from the same building, both engraved 

 under EGYPTIAN ARCHITECTURE, where also the female figures shown 

 in the cut of the temple of Abou-Sambul are supposed to be representa- 

 tions of Isis. 



As the worship of Isis passed into foreign lands it assumed a foreign 

 character and many foreign attributes, as we see from the Greek and 

 Roman writers. Sometimes Isis is represented like Diana of Ephesus, 

 as the universal mother, with a number of breasts. The mysterious 

 rites of Isis were probably hi their origin symbolical : on one of her 

 statues was the inscription, " I am all that has been, that shall be ; no 

 mortal has hitherto taken off my veil." But the Isiac rites, trans- 

 planted to Italy, became a cloak for licentiousness, and they were 

 repeatedly forbidden at Rome. Tiberius had the images of Isis thrown 

 into the Tiber, but the worship revived, and Juvenal speaks of it in 

 an indignant strain. The Isiac table in the Turin Museum, which is 

 supposed to represent the mysteries of Isis, has been judged by Cham- 

 pollion to be the work of an uninitiated artist, little acquainted with 

 the true worship of the goddess, and probably of the age of Hadrian. 



(Plutarch's Treatise on Isis and Osiris, Wyttenbach's ed., ii. 441 ; 

 Herod., ii. 41, 42, 123, &c. ; Pausan., ii. 13, 7, and particularly x. 32, 

 13; Rosellini; Wilkinson, Ancient Egyptians, vol. iv.) 



ISOCETAMIDE. [isocETic ACID.] 



ISOCETIC ACID (CjoH^OJ. The grains of several euphorbiaceous 

 plants yield by expression a white inodorous oil of sp. gr. '91. By 

 saponification with caustic soda it is separated into oleic and isocetic 

 acids. The latter purified by crystallisation from alcohol is obtained 

 in brilliant plates, the melting point of which is 131 Fahr. 



hncelamide (C, H, 1 NO.) results when the oil is heated with am- 

 monia in a closed tube. It is a white substance fusible at 152 and 

 not acted upon by concentrated caustic potash. 



Jiocetic ether is a white odourless body, solid at temperatures below 

 Fahr. [ETHEREAL SALTS.] 



ISOCHROMATIC LINES are those coloured rings which appear 

 when a pencil of polarised light is transmitted along the axis of a 

 crystal, as mica or nitre, and is received in the eye after passing 

 through a plate of tourmaline. If a plate of nitre, having its surfaces 

 perpendicular to the axis of the natural prism, and highly polished, be 

 placed between two plates of tourmaline having their axes at right 

 angles to one another, and the system be held close to the eye, which 

 is directed towards the sky or a sheet of white paper, there will be 

 seen a series of oval rings, about each of two points as poles, forming 



