weights, of 12.

using sulphuric acid.

This result confirms that obtained by

Exp. 4. Find the reacting weight of aniline; assuming that the double compound which this base forms with hydrochloric acid and platinic chloride has the composition 2XHCI. PtCl, where X = one reacting weight of aniline.

It is first necessary to purify the 'pure' aniline of commerce as follows. Equal masses (say 25 grams) of aniline and glacial acetic acid are mixed in a retort which is tilted upwards and attached to a long glass tube which serves as a condenser. The contents of the retort are heated to boiling for 12 hours, after which time the formation of acetanilide may be presumed to be complete. While the retort is still hot it is connected with a condenser, and heating is continued until the liquid which passes over begins to solidify. This will happen at about 280o-290o. The condenser is now removed and the receiver changed. The impure acetanilide which collects in the receiver is purified by recrystallising once or twice from a large quantity of boiling water. The acetanilide is reconverted into aniline by heating it with potash in a flask fitted with an inverted condenser, and the aniline is blown over with steam. The aniline is separated from the water as completely as possible, dehydrated by means of solid potash, and finally distilled; the portion boiling at 181°-182° is pure aniline. To this pure aniline is added a slight excess of hydrochloric acid, and the solution is evaporated to dryness at 100°; the residue is dissolved in a small quantity of water, and the liquid is filtered if necessary. To the filtrate a fairly strong solution of platinic chloride is added; but care must be taken that the platinum salt is not in excess. The double chloride of aniline and platinum which is precipitated is strained off from the mother liquor, and a small quantity is dried at 100° in a weighed crucible. The crucible plus dried salt is weighed; and the salt is then decomposed by heating it at first gently and finally strongly over a Bunsen-flame. The residual metallic platinum is weighed. Let w' weight of double chloride

=

and let X represent the reacting weight of aniline. Since the platinum double salts of nitrogenous bases are constituted on the same type as the platinum double salts of ammonia, it follows that 2XHCI. PtCl, represents the composition of the

aniline platinum chloride. The reacting weight of this double chloride is 2X + 73+ 339.5; on decomposition this mass would yield 197.5 of platinum. Hence the equation must hold

It is to be observed that this is a fairly general method for finding the reacting weights of organic bases.

Exp. 5. The reacting weight of iron-ammonium alum is expressed by the formula n(NH,Fe(SO,),.12H ̧O); find whether the value of n is 1 or 2.

If the formula which expresses the composition of a reacting weight of iron alum is (NH),Fe (SO), 24H,O it may be possible to partially dehydrate this compound and obtain the hydrate (NH),Fe (SO). H,O, whereas if the formula of the alum is NH ̧Fe(SO)2. 12H2O the composition of the lowest hydrate which could exist would be NH Fe(SO), H2O = (NH), Fe(SO,),. 2H,O.

Determinations of the ratio of the water lost to the solid remaining when iron alum is heated to different temperatures will therefore enable us to decide between the two possible formulae for this compound, provided it can be proved that dehydration is the only change which occurs when the alum is heated to these temperatures.

[Before beginning the Exp. read Lupton on The formulae of the alums, C. S. Journal, (2). 13, 201.]

Recrystallise some iron ammonium alum from water; powder a few grams, dry by pressure between paper, and at once weigh out about 5 gram into a small porcelain boat. Place the boat in a small hard glass tube; connect one end of the tube with a couple of drying bottles containing concentrated sulphuric acid and the other with bulbs containing Nessler's reagent for detecting ammonia. Arrange the tube in a small air bath fitted with a thermometer; draw a slow current of air through the tube, and heat to 150o until the weight of the substance in the boat is constant. Observe that ammonia is not given off during the operation. Then raise the temperature to 230° until no further loss of weight occurs, observing that ammonia is not evolved.

Having thus proved that the changes which occur at 150° and 230° are simple dehydrations, calculate the composition of

the salt which remained after heating to 150° and of that which remained after heating to 230°. Finally prove that moist ammonium sulphate evolves ammonia at about 120o125°.

Shew that your results confirm the formula

(NH), Fe(SO), 24H,O

for iron-ammonium alum.

The salt formed at 150° is (NH4),Fe2(SO4). H2O, and at 230o this is completely dehydrated.

Reference to "ELEMENTARY CHEMISTRY." Chap. VI. pars. 84 to 86; also Chap. XI. par. 163; also Chap. XVI. par. 315.

CHAPTER VI.

CHEMICAL CHANGE.

IN Part I. Chap. XVI. experiments were conducted to illustrate some of the conditions which chiefly affect the progress and final results of chemical reactions. Exp. 10 in that Chapter was conducted by causing solutions of ferric chloride and potassium sulphocyanide to react under conditions which were all constant except the relative masses of the reacting bodies; the amount of change increased as the mass of one of the reacting bodies increased relatively to that of the other.

The following experiment is performed with the same two compounds, ferric chloride and potassium sulphocyanide, but it is made quantitative.

Exp. 1. Prepare pure ferric chloride by passing a rapid stream of pure dry chlorine over pure iron wire heated to redness; resublime the chloride from a small tube of hard glass into a small bottle with a good stopper.

Prepare an aqueous solution of this ferric chloride of known strength; about 3 grams per litre is a convenient strength.

Experiments made by Gladstone shewed that when ferric chloride and potassium sulphocyanide interact in about the ratio Fe,Cl: 500KCNS the whole, or nearly the whole, of the ferric chloride is changed to ferric sulphocyanide. On the basis of this experimental result, prepare a standard solution of ferric sulphocyanide, by adding to a measured volume of the ferric chloride solution a quantity of potassium sulphocyanide such that the two salts are in the ratio Fe,Cl: 500KCNS. A convenient strength to make this standard solution is about 03 gram Fe(CNS), in 100 c.c.

Prepare a solution of potassium sulphocyanide, by dissolving a weighed quantity of the pure salt in water, of a strength such that equal volumes of this solution and of the solution of ferric chloride contain KCNS and Fe,Cl, in about the ratio 10: 1.

Now place a measured quantity, say 20 c.c., of the standard ferric sulphocyanide solution in a cylinder of white glass; into another exactly similar cylinder measure out small equal volumes of the ferric chloride and potassium sulphocyanide solutions, say 2 c.c. of each, the volume of ferric chloride solution containing exactly the same mass of ferric chloride as was used to prepare the volume of standard ferric sulphocyanide solution in the other cylinder.

Now add exactly enough water to make the total volume of the liquid equal to that of the standard solution in the other cylinder. The colour of the standard ferric sulphocyanide should now be considerably darker than that of the mixed solutions. Now run water from a burette into the standard solution until the depth of colour is the same in the two cylinders; measure the volume of water required.

2 6

Perform similar experiments, using in each the same volume of the ferric chloride solution, but increasing that of the potassium sulphocyanide solution; the ratio of KCNS: Fe,Cl, being (say) 10: 1, 15: 1, 20: 1, 40: 1, 80: 1, 100 : 1, and 200: 1. Calculate, in each case, (1) the mass of ferric sulphocyanide which would be obtained from the ferric chloride used supposing the whole of it were changed to ferric sulphocyanide; and (2) the mass of ferric sulphocyanide actually obtained. The second calculation is made by measuring the water added to the standard solution to make the depth of colour the same as that of the other solution, and then saying, as the total volume of the standard liquid is to the volume of this liquid before dilution, so is the mass of ferric sulphocyanide which would be formed if the whole of the iron salt had been changed to the mass of ferric sulphocyanide actually formed.

Arrange your results to shew the ratio of KCNS to Fe,Cl in each experiment, and the percentage of possible Fe,(CNS) actually produced.

The following examples are given to shew the kind of results obtained. 1.8194 grams FeCl were dissolved in 500 c.c. water: to 50 c.c. of this solution 27.27 grams KCNS were added and whole was diluted to 800 c.c. (this is called standard ferric sulphocyanide solution, ratio of KCNS