heated by means of a Bunsen-lamp furnished with a gas regulator and surrounded by a screen to stop draughts of air. The temperature of the glycerin is raised to 154°-156° and the tubes are then slowly immersed.

Six tubes, being two of each series, are removed at the end of an hour, and the remaining six are removed after 48 hours. When each tube is cold it is placed in a stoppered bottle containing 30-40 c.c. pure alcohol and 4 or 5 drops of a very dilute alcoholic solution of rosolic acid; the tube is broken by agitating the bottle, and the acetic acid which has not been decomposed is determined by the standardised baryta solution.

As the amount of acetic acid originally present is known, it is easy to calculate the percentage of acid, and hence the percentage of alcohol, which has been changed to an ethereal salt. The mean of each pair of experiments after etherification has proceeded for one hour is taken as the initial velocity of etherification, and the mean of each pair after 48 hours as the limit of etherification.

The experiments of Menschutkin proved that the systems consisting of acetic acid and ethylic, propylic, or butylic, alcohol attain their final equilibrium after about 48 hours at 155°. Menschutkin obtained the following results :-

The specific volume of a gasifiable compound is usually molecular weight

defined as

spec. grav. of liquid at B. P.

The specific volume of a solid compound is usually defined as reacting weight

spec. grav. of solid'

Determinations of these constants often throw light on questions regarding the constitutions of compounds. (s. Pattison Muir's Principles of Chemistry, Book I. Chap. IV. sect. 3.)

Specific volumes of liquids. Read, Ramsay on the Volumes of liquids at their boiling-points obtained from unit

volumes of their gases. C. S. Journal, Trans. 1879, p.

463.

Fig. 58 shews the apparatus required. It consists of (1) a small bulb of thin glass of about 10 c.c. capacity, sealed at one end, and terminating at the other end in a capillary tube bent into the form of a hook; (2) a glass vessel of the form, and about three times the size, of that shewn in the Fig. The bulb is suspended by thin platinum wire, as shewn; the exit tube from the glass vessel may be connected with a condenser if necessary.

The bulb is cleaned and dried, and its weight is carefully determined; it is then filled with boiled distilled water at a known temperature, and weighed; from these data, and the known expansion of water, the capacity of the bulb at 0° is determined. A little water is then placed in the glass vessel; the bulb (filled with water) is suspended as shewn in the Fig.; the water is boiled, and the bulb is allowed to remain in the steam until drops of water no longer flow from the capillary opening; the source of heat is removed and the bulb is allowed to cool; when cold, it is carefully dried externally, and weighed. The results of this experiment afford data for finding the correction to be applied for the expansion of the glass of the bulb, and for the difference between the temperature of a liquid in the bulb suspended in the vapour obtained by boiling that liquid in the glass vessel and the true boiling point of the liquid. The calculation is made by finding the volume at 100° of the water contained by the bulb at 0°, from the data of Regnault and Kopp, and comparing this with the observed volume of the water contained by the bulb when heated in steam: the result is stated in the form of a coefficient*.

Fig. 58.

The bulb is now emptied, by placing its open end downwards and heating, rinsed with alcohol, and dried; a little of the liquid the specific volume of which is to be determined is Ramsay found that the coefficient for almost every bulb is 00015. One volume of water at 0° becomes 1.042986 vols. at 100o.

*

now brought into the bulb, by warming and at once plunging the open end into the liquid; the bulb is rinsed with this liquid and then emptied, and this process is repeated two or three times. The bulb is now nearly filled with the liquid to be examined, by introducing a little as described, boiling this by means of a lamp or by surrounding it with hot sand, and plunging the open end into the liquid, and repeating this process until sufficient liquid is got into the bulb. Should the liquid to be examined be very volatile, or be decomposed by air or moisture, it is advisable to fill the bulb by suspending it in the glass vessel, inserting a glass rod in place of the exit tube from the vessel, and connecting the lower end of the bulb with this rod by a platinum wire; some of the liquid is then quickly brought into the glass vessel and boiled; the bulb being thus heated is lowered into the liquid and tilted, by means of the two wires and glass rods, so that its neck is beneath the level of the liquid for a moment; a little liquid enters; the bulb is raised and the liquid is boiled; this process is repeated till sufficient liquid has been got into the bulb.

When the bulb has been nearly filled with the liquid whose specific volume is to be determined, it is suspended in the glass vessel, in which is placed a little of the same liquid; the liquid in the vessel is boiled; when drops no longer flow from the capillary opening of the bulb, the boiling is stopped; the bulb is allowed to cool, when it is dried and weighed.

The specific gravity of the liquid at its boiling point is calculated by the formula ;—

=

where W' weight of liquid in the bulb, W = weight of water which fills the bulb at 0°, t = boiling point of liquid, and a = a coefficient as determined by experiment (usually about 00015).

The student should determine the specific volumes of (1) ethylic alcohol, (2) a paraffin or olefine boiling from 40° to 90°, (3) benzene, (4) phenol.

Specific volumes of solids. Read Thorpe and Watts on the Specific volumes of water of crystallisation. C. S. Journal, Trans. 1880, p. 102.

A stoppered specific gravity bottle of 25 c.c. capacity with a narrow neck, and several small weighing tubes, must be provided. The bottle is carefully cleaned, dried, and weighed, these processes being repeated two or three times. It is then

filled to the mark on the neck with benzene which has been purified by freezing, and immersed in water of a known temperature for some hours; the level of the benzene is then accurately adjusted to the mark on the neck, and the bottle is dried and weighed. This process is repeated several times. The data for the bottle are thus obtained.

The compounds whose specific volumes the student is asked to determine are, copper sulphate and its various hydrates, cupric hydroxide, and cupric oxide.

(a) Copper sulphate; CuSO. Pure copper sulphate is recrystallised from water. The crystals are powdered and dried, and a weighed quantity is heated to 280°, in watch-glasses, until it ceases to lose weight. The dry salt is then transferred to one of the weighing tubes and placed in the air bath at 280°; after a little time the tube is removed to an exsiccator and allowed to cool; a few grams of the salt are then quickly transferred to the specific gravity bottle; the bottle and its contents are heated to 280° until the weight is quite constant. The bottle is filled with benzene, and the necessary weighings are made. Two independent series of observations should be made.

(b) Pentahydrated copper sulphate; CuSO4.5H2O. Prepared by re-crystallising pure copper sulphate from water, powdering, and drying by pressure between filter paper.

The specific gravity is determined as described, but it is not necessary to heat the bottle or the salt.

2

(c) Trihydrated copper sulphate; CuSO,. 3H,O. Pour a cold saturated solution of pure copper sulphate into an equal volume of sulphuric acid of specific gravity 17; wash the pp. which forms with small successive quantities of absolute alcohol until the washings are free from sulphuric acid, and dry between filter paper. Make determinations of the water, by drying at 280°, and the sulphuric acid, by precipitating as BaSO.

The specific gravity is determined as in (b).

(d) Dihydrated copper sulphate; CuSO. 2H,O. Pour a cold concentrated solution of pure copper sulphate into concentrated sulphuric acid with constant stirring; wash with absolute alcohol, and dry between filter paper. Make determinations of the water and sulphuric acid.

The specific gravity is determined as in (b).

(e) Monohydrated copper sulphate; CuSO.H,O. Heat the pentahydrate to 110° until it ceases to lose weight at that temperature. Make a determination of sulphuric acid, or of water.

Determine the specific gravity as in (a), heating the specific gravity bottle with the salt in it to 110° until the weight is

constant.

(f) Cupric hydroxide; CuO,H,. Add potash to a cold rather dilute solution of pure copper sulphate until the blue colour of the liquid has nearly disappeared; collect the pp. on a filter, wash it as rapidly as possible with cold water until the washings are free from sulphates, dry by pressure between filter paper and then over sulphuric acid. Make determinations of water by heating to redness, and of copper by standardised potassium cyanide solution.

The specific gravity is determined as in (b). (g) Cupric oxide; CuO.

Heat a portion of the hydroxide (f) to 150°-200° until it ceases to lose weight. Determine the specific gravity as in (b).

Assuming that the differences between the specific volumes of the various hydrated copper sulphates represent the specific volumes of the water of crystallisation combined with copper sulphate to form these various hydrates, and that the difference between the specific volumes of CuO and CuO,H, represents the specific volume of the water of constitution which chemically interacts with CuO to form CuOH2, compare the results you have obtained in exps. (a) to (e) with those obtained in exps. (ƒ) and (g), and shew how they help to establish a distinction between water of crystallisation and water of constitution. As additional data in this comparison make use of the following specific gravities of oxides and hydroxides or hydrated oxides ;—

Calculate in each case the mean specific volume of each molecule of water of crystallisation, and compare this volume with the mean specific volume of each molecule of water of constitution.

The following are the values obtained by Thorpe and Watts for the spec. volumes of copper sulphate and its different hydrates ;-M= CuSO4.