400 



THE POPULAE EDUCATOE. 



with the hydrogen of the fat, forming hydrochloric acid (HC1). ' 

 The carbon comes away unburnt as smoke. 



Bodies rich in hydrogen will frequently take fire when 

 plunged into a jar of this gas. This is the case with a piece 

 of paper dipped in turpentine. Metals in a finely divided 

 state are violently attacked by the gas. Copper leaf and 

 antimony, which is powdered and slightly warmed, even take 

 fire, the result being in every case a chloride of the metal. 



The peculiar affinity chlorine possesses for hydrogen gives it the 

 power of bleaching. If grass and fabrics dyed with vegetable 

 colours be dipped into a jar of the gas, they will become white. 

 This will be found to be the case only when the articles are 

 moist; then the chlorine, taking the hydrogen of the water, 

 liberates the oxygen, which, being in its nascent state, is much 

 more active, and attacks the colouring matter, thus bleaching 

 the body. This may be well illustrated by dissolving some 

 indigo in sulphuric acid, and adding to a dilute solution some 

 of the chlorine water above mentioned. The colour entirely 

 disappears. The difference between writing ink and printers' 

 ink is shown by introducing each into a jar of this gas ; the 

 former is bleached. 



This property of chlorine makes it valuable as a disinfecting 

 agent. It attacks the hydrogen of the noxious gas, and thus 

 destroys it. 



Hydrochloric Acid (symbol, HC1 ; combining weight, 36'5 ; 

 density, 18'25). This liquid is also called muriatic acid, or 

 spirits of salt ; it is water largely impregnated with the gas 

 hydrochloric acid, which is prepared by gently heating common 

 salt and sulphuric acid in a flask : 



NaCl + H 2 S0 4 = HC1 + NaHS0 4 . 



The gas which comes off is colourless, 1'27 times heavier than 

 the air, and possesses a pungent odour. In contact with the 

 air it combines with moisture, giving rise to white fumes. At 

 a pressure of 40 atmospheres it becomes a clear liquid. Its 

 composition may be determined both synthetically and ana- 

 lytically by the eudiometer. If equal volumes of chlorine and 

 hydrogen be introduced into the instrument, on the passing of 

 the spark they combine, forming HC1. There is no diminu- 

 tion of volume. Thus 



H 4- Cl = HC1 

 1 + 1=2. 



If now a series of electric sparks be passed, some of the gas 

 is again decomposed, and the unaltered acid may be removed 

 by allowing a few drops of water to rise up through the mercury ; 

 these absorb the undecomposed HC1. The remaining gas is 

 found to be equal volumes of H and Cl. These gases, when 

 mixed in equal proportion, will combine, with an explosion, in 

 sunlight. 



Large quantities of this acid are made as a bye product in 

 the manufacture of sodium carbonate. In this, its commercial 

 state, it is very impure, since it contains iron in the form of a 

 chloride, to which its yellow colour is due, and also sulphuric 

 acid and arsenic. 



The result of the action of hydrochloric acid on metals is 

 that chlorides of the metals are formed. Their various salts 

 may be found by replacing the H in the HC1, according to the 

 atomicity of the metal. The presence of a chloride in a solu- 

 tion may be at once detected by a few drops of silver 'nitrate. 

 The white, curdy silver chloride falls. 



Aqua regia is a mixture of nitric and hydrochloric acids, 

 which is capable of dissolving both gold and platinum. 



Oxides of Chlorine. Although these elements do not combine 

 by direct means, yet in indirect ways five compounds have been 

 produced : 



Hypochlorous acid 

 Chlorous acid . 

 Peroxide of chlorine 



HC10 

 HC10 



Chloric acid . 

 Perchloric acid 



HC1O, 

 HC1O. 



Hypochlorous Acid (HC10). The prefix " hypo " is from the 

 Greek faro, under, or beneath, signifying that this acid has less 

 oxygen in it than chlorous acid. It may be obtained by shaking 

 up mercuric oxide with chlorine water. The reaction is 

 HgO + 2C1, = C1,O + HgCl,. 



The C1 2 is hypochlorous oxide. This combines with an atom 

 of water, forming the hydric salt, or the acid 



H,0 + C1,O = 2HC10. 



The acid has a sickly odour, and is extremely weak, carbonic 

 acid being capable of ejecting it from its combinations. 



It is chiefly noted as a powerful bleacher, being the active 

 principle in bleaching powder, which is a mixture of calcium 

 chlorite (CaCl ? ) and hypochlorite (CaCl 2 O 2 ), and is made by 

 allowing chlorine to enter the top of a chamber in which are 

 trays of well-slaked lime one above the other. The gas falls 

 by its weight, and is absorbed by the lime. 



Chloride of lime, as this compound is usually called, emits 

 the odour of hypochlorous acid. When exposed to the air, 

 carbonic acid gradually displaces the chlorine which is given 

 off. This makes this substance a valuable disinfectant, as the 

 quantity of the gap emitted is so small as not to be injurious, 

 and yet effective. The best mode of using it is to dip cloths iff 

 a solution of the powder, and hang them up. 



Chloride of lime is used as the great bleacher. The calico, 

 etc., is boiled in lime-water and a weak solution of caustic soda, 

 to remove the grease of the manufacture and the "dressing." 

 It is then soaked in a solution of two and a-half per cent, of 

 bleaching powder in water. But the action is not discernible 

 until the fabric is " soured " or dipped in a weak solution of 

 sulphuric acid and water. Thus the chlorine is liberated in the 

 fibre of the cloth, and the bleaching is effected. Sometimes 

 this process is repeated, and finally the articles are thoroughly 

 washed in water to remove all traces of the acid. 



Chlorous Acid (C1 2 3 ). To prepare this gas, three parts of 

 arsenious acid, and four of potassium chlorate, 

 are made into a paste with water ; sixteen 

 parts of pure nitric acid (specific gravity, l - 24) 

 are added ; the whole is placed in a small flask, 

 which is filled up to the neck with the mixture, 

 and a very gentle heat applied by means of a 

 water-bath. The yellow-green gas may be 

 collected in dry bottles by displacement. The 

 greatest care is required in its manipulation, 

 as it explodes at a temperature of about 56 

 Cent., and also if it come into contact with 

 any very combustible body. Its formation is 

 due to the deoxidisation of the chloric acid 

 in the potassium chlorate. 



Peroxide of chlorine (C1 2 OJ is a gas which 

 explodes as soon as it touches organic or com- 

 bustible bodies. It is prepared by pouring 

 sulphuric acid on potassium chlorate. Mix 

 equal parts of sugar and potassium chlorate, 

 each in powder ; then pour upon them a few drops of sulphuric 

 acid ; the whole will ignite. On this principle the first attempt 

 at matches was founded. 



Place a piece of phosphorus about the size of a pea at the 

 bottom of a tall glass full of water (Fig. 43), also add a few 

 grains of potassium chlorate ; through a long tube pour a little 

 sulphuric acid to the bottom of the glass. The phosphorus enters 

 into combustion with the peroxide of chlorine as it escapes. 



Chloric Acid (HC1O 3 ). This acid forms chlorates : if a current 

 of chlorine gas be passed through a strong solution of caustic 

 potash, the following reaction ensues : 



3Cl a + 6KHO = KC1O. + 5KC1 + 3H 2 O, 



potassium chlorate and chloride being the result ; as the latter 

 is more soluble, therefore it can easily be separated from the 

 chlorate by crystallisation. It will be remembered that potas- 

 sium chlorate was used in the preparation of oxygen. 



Perchloric Acid (HC10 4 ). If the decomposition of potassium 

 chlorate when giving off oxygen be stopped, the residue will be 

 found not only to contain potassium chloride and chlorate, but 

 also perchlorate. It may be separated by means of hydrochloric* 

 acid, which acts on the chlorate and decomposes it, but not on 

 the perchlorate. From this salt the acid itself may be got. 



Compounds of Chlorine and Nitrogen. If chlorine be passed 

 into ammonia, as has before been said, nitrogen is liberated ; 

 but after a certain quantity of sal-ammoniac has been produced, 

 drops of an oily liquid begin to form. These are supposed to 

 be the terchloride of nitrogen (NC1 3 ), the most explosive and 

 the most dangerous of chemical compounds. The experiment 

 should never be attempted, unless all the apparatus used be of 

 lead, and the operator dressed in a strong suit of leather, with 

 an iron mask. A drop of this substance in a porcelain capsule 

 was touched with the top of a fishing-rod ; the violence of the 

 explosion drove some of the porcelain through the bottom of the 

 chair, which was of thick wood. A kindred compound of nitrogen 

 with iodine, which is not so explosive, will be noticed. 



Pig. 43. 



