318 



OHBMIST&Y. 



[lolUNK AND IIHOMINE. 



chloridei of those substances, the two best known being 

 the common salt and sal-ammoniac. It forms chlo- 

 ride* with metallic bases, uniting with them in various 

 rtioui in that of one equivalent, a* in chloride of 

 ilvcr, or in three, a* in the terchlorido of gold. The 

 Muting between that of chlorine to bases 

 is similarly distinguished to those of oxygen.* Generally 

 speaking, the chlorides are soluble in water ; but this 

 : --rty varies considerably : thus chloride of potassium 

 dissolves readily ; whilt the chlorides of mercury are 

 almost, or comparatively insoluble. The affinities of 

 chlorine for its bases are generally very active, and 

 second only to those of oxygen, which, therefore, mostly 

 has the power of seizing the bases of the chlorides, :in<l 

 of setting the chlorine free, or leaving it to combine with 

 some other substance. The various combinations of 

 chlorine, forming chlorides, will be described in con- 

 nection with their different bases. 



Chlorine combines with oxygen to produce various 

 compounds ; such as enchlorine, chlorous, hypochlorous, 

 hypuchloric, chloric, and perchloric acids. Of these, the 

 chloric is the most important in all respects ; for it gives 

 rise to the chlorates, some of which are largely employed 

 for the manufacture of lucifer-matches, <tc. Hypo- 

 chloric acid is prepared by adding sulphuric acid to 

 chlorate of potass ; but as this product is dangerously 

 explosive, only very small quautities (grains) of the 

 ingredients should be employed ; and then only in an 

 open vessel. The acid is liberated in the form of a gas, 

 which may be condensed by frigorific mixtures. We 

 would warn our readers against attempting to use a 

 test-tube for the purpose, having nearly lost the use of 

 one eye whilst doing so ourselves. 



Chloric acid is a compound of one equivalent of 

 chlorine with five of oxygen; symbol Cl Os; equiva- 

 lent = 75 '5. It may be obtained by adding sulphuric 

 acid to a solution of chlorate of baryta, which, like the 

 chlorate of potash, is obtained by passing gaseous chlo- 

 rine through a solution of the earth ; the chlorate of 

 potash being produced by passing the gas through a 

 solution of that alkali We have to speak more fully of 

 these salts hereafter, both as to their manufacture and 



Perchloric acid is a combination of seven equivalents 

 of oxygen with one of chlorine ; and as it is of no great 

 intermit, we shall omit details of its manufacture. 



A compound acid is produced by adding together two 

 parts, in volume, of hydrochloric acid, with one of nitrio 

 acid, both in as high a degree of concentration as 

 possible. The mixture is called aqua regia, and it is 

 in IK h used by metallurgists for the solution of gold. 

 I'latina and other metals are soluble in it ; and it pro- 

 duces their chlorides, which will be duly noticed here- 

 after. 



IODINE. 



TUB discovery of iodine at first arose from an accidental 

 circumstance, and is of comparatively recent occurrence. 

 It was noticed that the pans in which banlla had been 

 manufactured, became very much corroded in some 

 parts; and, eventually, chemical research accounted for 

 the fact by showing the presence of a substance pre- 

 viously unknown as a distinct body. Iodine, as usually 

 met with in commerce, is a substance in small metal -like 

 scales, of a dark colour. On being heated, it affords a 

 vapour of a rich purple tint hence its name. The 

 vapour condense*, and re-forms scaly {articles. The 

 symbol is I, and the equivalent 127. As has been 

 already named, its combinations are termed iodides. 



l-'-r many years the uses of iodine were entirely con- 

 fined to medical purposes, and especially as an antidote 

 reventative for the troublesome disease called 

 Its presence in cod-liver oil has, doubtless, been 

 hi.-lily beneficial in scrofulous and phthisical complaints. 

 It is of ten administered in the form of its combination 

 with oxygen and potass, ax the hydriudatu of potass. 

 Since the discovery of photography, it has become of 



Set (, p. lit. 



great importance ; and, as such, in now a considerable 

 product of tin- II|K-I I .i^t's manufactures. The 



chief of its combinations, employed in photography, are 

 the iodides of potassium, ammonium, and cadmium. 

 Holt of the compounds of iodine are readily decom- 

 posed by chlorine, to which it ranks next in importance 

 with respect to its chemical characters and allinities. 

 The following experiments will give a general idea of 

 some of its leading properties. 



Experiment 2C. Put a small quantity of commercial 

 iodine into a clean I :i.isk, and apply a gentle 



heat by means of the spirit-lump. The i-'iin.- will 

 as a purple vapour, and will eVfiituallycuiHlcn.se on the 

 cold sides or neck of the flask, in minute, dark-coloured 

 crystals or plates. 



Ex/* riment 27. Dissolve a little iodide of potassium 

 in aid water, and add a small portion of starch. No 

 change will take place ; but, on pouring into the solu- 

 tion a little sulphuric acid, the iodine will be set free, 

 and a dark-blue colour will be observed. Starch is 

 generally used as a test for the presence of free iodine ; 

 but the effects of the test are not evident if the solution 

 be hot Similarly, the presence of starch in vegetable 

 matter may be detected by means of iodine. 



Iodine combines readily with some of the metals, either 

 in its state of vapour, or when in combination with other 

 bodies, as the following experiment will show. 



Experiment 28. Expose a plate of silver to the 

 vapour of iodine ; a yellow iodide of silver will soon be 

 formed on its surface. In this manner iodine was ex- 

 tensively employed on silver plates for the Daguerreotype 

 process, which was, at one time, the chief method of 

 obtaining pictures by the action of light. 



Experiment 29. Add a little of the solution of iodide 

 of potassium to one of the bichloride of mercury in 

 water ; a yellow precipitate of iodide of mercury will be 

 produced. On the addition of more of the iodide of 

 potassium, the yellow colour will change to a deep red ; 

 and on a still further addition, the precipitate will be 

 entirely redissolved ; the iodide of mercury being soluble 

 in an excess of that of the iodide of potassium. 



Iodine is but slightly soluble in water ; but Ls readily 

 dissolved by alcohol, which thus forms what is termed 

 the tincture of iodine, much used in medicine. It 

 unites with chlorine, bromine, nitrogen, ami hydrogen ; 

 forming with the latter an acid the hydriodic. With 

 nitrogen, it produces an explosive compound, which is 

 analogous to the chloride of nitrogen, of which we shall 

 treat on hereafter. It unites also with sulphur and 

 phosphorus, producing light and heat at the moment of 

 its combination with tho latter substance : an explosion 

 is afforded ; hence great care is required when these 

 substances are brought into contact. Iodine may 

 readily bo set free from its combinations l>y means of 

 chlorine, as is illustrated in the following experiment. 



Experiment 30. Dissolve some iodide of imiassium in 

 water, and add a little starch or arrowroot. I 'our into 

 this a solution of chlorine in water, t The iodine will In 

 at once set free, and the starch be converted to a blue 

 colour. 



Hydriodic acid is a combination of one equivalent each 

 of iodine and hydrogen ; symbol, IH ; equivalent, 128. It 

 is prepared from iodide of phosphorus. Iodine unites 

 with oxygen in three forms ; tho most important of which 

 is iodic acid, which is composed of one equivalent of 

 iodine to five of oxygen ; symbol, IO ; equivalent, 1G". It 

 forms iodates with bases, which are analogous to the 

 chlorates and bromates ; they have no special application 

 in the arts and manufactures. 



The remaining combinations of iodine will be noticed 

 in connection with their bases. 



BROMINK. 



BROMINE, like iodine, is a product of kelp, and is found 

 in sea-water, in the salt called bromide of sodium, <bc. 

 It is a den-c' orange-ooloured liquid ; has an otf'ensivu 

 smell hence its name ; and is corrosive in its action on 

 t See ante, p. 316. 



