916 IODINE 



for being incorporated with the purified lamp-black. The astringent principle in 

 vegetables does not precipitate gelatine when its acid is saturated, as is done by 

 boiling the nut-galls with lime-water or magnesia. The first mode of making the ink 

 is to be preferred. The lamp-black is said to be made in China, by collcc-ting the 

 smoke of the oil of sesame. A lit i In < unphor (about 2 per cent.) has been detected in 

 the ink of China, and is supposed to improve it. Infusion of galls renders the ink 

 permanent on paper. 



Printing Ink. This is essentially a combination of lamp-black finely-divided 

 carbon with oil. Mr. Underwood, in a communication made by him to the Society 

 of Arts, well defines the necessary qualifications of a good ink : 



1. It must distribute freely and easily, and work sharp and clean. 



2. It must not have too much tenacity for the type, but have a much greater affinity 

 for the paper, and so come off freely upon it. 



3. It must dry almost immediately on the paper, and not dry at all on the type or 

 rollers : this is a great desideratum, especially for newspapers. 



4. It should be literally proof against the effects of time and chemical reagents, and 

 never change colour. 



Great attention must be paid to the quality of the linseed-oil employed, and even 

 the character of seed from which the oil is obtained should not be neglected. 



The linseed-oil is clarified from the fatty matters, and the pure oil is boiled 

 with great care at a carefully-regulated temperature ; and, during the boiling, the 

 best pale yellow soap is added to give it consistency, and the required dryers aro 

 also now mixed with it. The best black is that obtained from the smoke of naphtha, 

 the combustion being carefully regulated. This black is ground up carefully with 

 the drying oil, which has assumed the character of a varnish, and the ink is complete. 



IKTiiUJG-ROLLER. See PRINTING. 



ITJOSITE. A variety of glucose, or grape-sugar, occurring in the muscles of the 

 heart and of certain other organs. It is also found in the kidney-bean, whence it is 

 sometimes termed phaseomannite. 



IKTSTANTAMTEOUS MATCHES. See MATCHES. 



INUXiXlff. A substance similar in its properties to starch, discovered by Rose 

 in 1804. It has been obtained from elecampane root, potato and dahlia tubers, from 

 dandelion roots, and many other similar plants. See Watts's ' Dictionary of Chemistry.' 



INVERTED SUGAR. A peculiar kind of sugar, formed by the prolonged 

 boiling of ordinary cane-sugar with water. 



XODXC MERCURY. See MERCURY. 



IODIDES. Compounds of iodine with metals or radicals. The more important 

 are described under the respective metals, as iodide of potassium, under POTASSIUM. 



IODINE (lod, Fr. ; Jod, Ger.) is one of the elementary substances ; it was 

 accidentally discovered in 1812 by M. Courtois. a manufacturer of saltpetre at Paris. 

 He found that, in the manufacture of soda from the ashes of seaweeds, the metallic 

 vessels in which the processes were conducted became much corroded ; and in search- 

 ing for the cause of the corrosion, he discovered this now important substance. It 

 was first described by Clement in 1813, but was afterwards more fully investigated 

 by Davy and Gay-Lussac. 



Gay-Lussac and Clement at first regarded hydriodic acid as hydrochloric acid, 

 until Sir H. Davy suggested the idea of its being a new and peculiar acid, and iodine 

 as a substance analogous in its chemical relations to chlorine. 



It was named iodine from the Greek word twSrjy, violet-coloured, on account of the 

 colour of its vapour. 



Iodine exists in many mineral waters, in combination with potassium and sodium. 



In the mineral kingdom, iodine has been found in one or two rare ores, as in a 

 mineral brought from Mexico, in which it existed in combination with silver, and also 

 in one from Silesia in combination with zinc. See IODITK. 



It exists also in very small quantities in sea-water, from which it is extracted by 

 many seaweeds, which act therefore as concentrators of iodine; these seaweeds, wlu-n 

 dried and ignited, yield an ash, technically called kelp, from which all the soda of 

 commerce was previously obtained, but the chief value of the kelp now is on account 

 of the iodine which it yields. The following is the process most generally adopted for 

 the extraction of the iodine from the seaweeds : 



The sun-dried seaweed is incinerated in shallow excavations at a low temperature, 

 for, if the temperature was allowed to rise too high, a considerable quantity of iodide 

 of sodium would be lost by volatilisation. The half- fused ash or kelp which remains 

 is broken into fragments, and treated with boiling water, which dissolves about one 

 half of the ash. 



The liquid thus obtained is evaporated, when, on cooling, the more crystalli.sablo 

 salts separate, viz., sulphate and carbonate of soda, with some chloride of potas- 



