LESSONS IN CILEMI8TEY. 



stances. In other i . -peotn its form in seal-like, having a short 

 ly broadest round the ehest. and dii:. 



lillllis. 'I'll.' inxidit ..i tin- Hipper* 



horny kind of coat, whioh may have bn-n pro- 



;ml>ing over rooka and ice. It in ten 



Ion?, some of the largest bulls eveu attaining to 



ity foot. Tho colour, according to Pabricius, 



with tlio ago, the young being black, then becoming 



and gradually paler and paler till thu animal in old age 



i ins is direetly opposite to the order of colour- 



observed in a great numbor of other animals ; oven in 



man, for example, whose hair as a child may be of a light 



but on reaching manhood has become decidedly darker. 



Thu ehanu'e in tin- walrus is probably one which is induced by 



unatic conditions it has to withstand, and, in becoming 



paler and p.iler as it increases in years, it is but obeying that 



mysterious law that animals have to acquire the colour of their 



surrounding, so that Arctic animals ought by rights to be as 



whito aa the ice and snow they move on. 



1 lie walrus is rare on the coasts of Britain, but in the North 

 Pacific Ocean they may be observed lying in hundreds on the 

 ire, huddling over ono another like swine, and roaring and 

 braying loudly. Mariners have often been warned by their 

 noise of the close proximity of the ice, when the dense fog 

 rendered everything a short distance away quite indiscernible. 

 It feeds mainly on shelled molluscs, which it rakes from the 

 submerged soil with its tusks. The tusks are likewise useful 

 in enabling it to pull itself up on to the shore. In swimming, the 

 fore and hind limbs take part in the work in nearly equal 

 degree, the flippers being moved alternately, and the hind 

 extremities being lashed from side to side by a twisting curved 

 motion. 



Their tusks supply us with an ivory harder and whiter 

 than that of the elephant ; an oil of better quality than the 

 whale's is extracted from their fat ; and their skins when tanned 

 make a thick and substantial leather. The walrus is therefore 

 much hunted, and, being exceedingly bold when attacked, the 

 pursuit is one of no small danger. 



LESSONS IN CHEMISTRY. XIII. 



COMPOUNDS OF CARBON WITH NITROGEN AND SULPHUR 

 THE HALOGENS CHLORINE. 



CARBON forms other compounds than those with oxygen and 

 hydrogen already described. It enters into combination with 

 chlorine, but the four products will not require attention until 

 we reach organic chemistry. Only ono compound is known with 

 nitrogen. It is 



Cyanogen (symbol, CN; combining weight, 26; and the density 

 has been found to be 26, and therefore its true symbol is CjN.,). 

 It was discovered in 1814 by Gay Lussac, and derives its 

 name, " a producer of blue," from the fact that it is the chief 

 agent in the production of Prussian blue. When bodies which 

 contain carbon, nitrogen, and potash are heated together, a 

 remarkable salt, the cyanide of potassium (KCN), is formed, 

 which is characterised by crystallising in large yellow tables. 



To produce this, substances rich in nitrogen such as hoofs, 

 hide-clippings, woollen rags, dried blood, etc. are heated in an 

 iron pot with two and a-half times then- weight of potassium 

 carbonate. Tho resulting potassium cyanide is now dissolved 

 out by water and allowed to crystallise. It is commonly called 

 the prussiate of potash. When iron, or any of the proto-salts 

 of iron, is added to a solution of this prnssiate of potash, 

 largo four-sided tables are deposited, which are ferrocyanide 

 of potassium. When ten parts of this salt are dissolved in 

 four times their weight of warm water, and distilled vrith seven 

 parts of sulphuric acid diluted with twice its weight of water, 

 the tirst portion of the liquid whioh comes over is a dilute solu- 

 tion of hydrocyanic orprussic acid (HCN). Mercuric cyanide may 

 be made from this by saturating the solution with red oxide of 

 mercury, and then evaporating. If this salt be heated, it is 

 decomposed into cyanogen and mercnry ; and thus it is we get 

 the compound. It is found to be a transparent, colourless gas, 

 poisonous and inflammable; its flame is edged with purple; 

 being soluble in water, it must bo collected over mercury. 

 If the gas bo passed through iron tubes at a high temperature, 

 it is decomposed, charcoal is deposited, and, as might bo 



anticipated from the following equation, the 

 U of the same volume an tho original 



C.H. - C. + K. 



a -- +. 



When a solution of ferrocyanide of potassium is iKH+d to 

 nolution of a sesquiaalt of iron, the well-known Prussian bine u 



Hij'lrc.j,inic acid (HCN) ha* been alluded to, and the ftrtt 

 stage of ita preparation given. If it be required in iU pore 

 state, dry calcium chloride U added to the above eolation, and 

 thu liquid distilled. Thia most never be attempted ave by 

 . \p i i. need persons, and only then for some good reason. It 

 is tho most powerful poison known. It in a limpid, cokmrlese 

 liquid, which gives off vapour, a breath of which would be fatal. 

 The poison seems to attack and prostrate the nenral system, 

 and in cases where death has not resulted, the treatment is to 

 pour cold water down the spine. 



The acid has the odour of almonds, for in the kernels and 

 leaves of many plants it i. found in minute quantities. 



There are other compounds of carbon and nitrogen into which 

 oxygen enters, but they become too complicated for an el emeu- 

 tary study of chemistry. 



Bisulphide of Carbon (symbol, CS,j combining weight, 76; 

 density, 38). A porcelain tube is passed through a charcoal 

 furnace in an inclined position ; it is packed with charcoal , 

 occasionally, into its upper end, pieces of sulphur are thrown, 

 and then the tube is stopped up by a cork. The sulphur in 

 vaporised, and combines with the carbon, forming tile bisul- 

 phide of carbon. A glass tube attached to the lower end of 

 the porcelain tube conducts the vapour into a condenser, which 

 is kept cool. Here there collects a mobile liquid of a very 

 high refractive power, and possessing a fetid odour. It dissolves 

 sulphur and phosphorus. This latter solution is the " Fenian 

 fire," for when a bottle of it breaks, the bisulphide rapidly 

 evaporates, depositing the phosphorus in so finely divided a state, 

 that it soon spontaneously ignites. It also acts aa a solvent on 

 gums and india-rubber. 



THE HALOGENS. 



There are four elements which closely resemble each other, 

 and which, from the fact that they combine directly with the 

 metals to form salts, have received the name of halogens, "salt- 

 producers." These elements are chlorine, bromine, iodine, and 

 fluorine. 



CHLORINE (symbol, 01 ; combining weight and density, 

 Chlorine is the most prominent member of the group. 

 very widely disseminated through Nature, in combination with 

 'sodium, with which metal it forms common salt (NaCl). 



Preparation. There are two ways by whioh this gas may be 

 obtained : 



1. Dilute sulphuric acid with its own bulk of water ; allow u 

 to cool, then to fourteen parts of this in a Florence flask add 

 four parts of common salt, intimately mixed with three part* of 

 black oxide of manganese. This reaction will ensue 



2H.SO. + 2NaCl + MnO, = Na.SO. + MnSO. + 2H,O + SCL 



2. If hydrochloric acid bo added to black oxide of msnganess, 

 the effect will be the liberation of chlorine, thus 



MnO, + 4HC1 = MnCl, + 2H.O + 9CL 



The gas is greenish yellow, hence ita name, and is about two 

 and a-half times heavier than air. When submitted to a 

 pressure of four atmospheres, it becomes a liquid, which as yet 

 has aever been frozen. Tho gas is best collected in the usual 

 way, but the water must be trarm, for cold water absorbs twicv 

 its bulk of the gas. Such a solution is a very convenient way 

 of keeping chlorine for test purposes. The bottle may 1*> 

 labelled " Chlorine water," and kept well stoppered and in the 

 dark, for light causes the chlorine and the hydrogen of the 

 water to combine. On account of its weight, the gas may also 

 bo collected by " displacement," by passing the delivery tube 

 to the bottom of the jar. 



It will bo found to possess a most irritating odour, and 

 if breathed in any quantity may produce uloeration of the 

 lungs. Since it does not combine directly with oxygen, 

 chlorine is not combustible ; but its most distinctive property 

 is ita great affinity for hydrogen. If, therefore, a toper I- 

 introduced into a jar of tho gas, it will burn with a smoky 

 flame. The combustion is due to the combining of the uhkais* 



