One part is soluble

Solubility of Official Chemicals in Water and in Alcohol.—(Continued.)

Chemicals.

Sodii Nitris

Strychnina

Strychnine Sulphas

Sulphur Lotum

Præcipitatum

Sublimatum

Sulphuris Iodidum

SOLUTION OF GASES IN LIQUIDS.

The methods employed to effect the solution of gases in liquids differ

FIG. 223.

essentially from ordinary processes of solution, and depend upon the solubility of the gas in the liquid, the relative specific gravity, and the strength of the solution desired. It is usually sufficient to conduct the gas into the liquid by a suitable tube, reaching nearly to the bottom, when more or less of the gas is absorbed by the liquid. Fig. 223 shows a simple method where the gas is readily soluble in the liquid, as in making chlorine water. For a continuous operation, as in making hydrochloric, nitric, and hydrobromic acids, and similar liquids, the well-known Woulffe's, or three-necked, bottles are employed advantageously, the gas which escapes solution in one bottle passing over into the next. The washing-bottle shown in Fig. 224 is easily made, and well adapted for purifying the gas after it is

Method of absorbing gas.

generated. B is an ordinary wide-mouthed bottle, closed with a perforated rubber cork, C; a wide tube, DE, passes nearly to the bottom, and a narrow tube, A, is joined by a short piece of rubber tubing, J, to the tube leading from the generating flask, and at the other extremity is curved upward so as properly to deliver the gas into the water placed in the bottle to wash it: it escapes by the bent tube, T, which is continued until it dips into the liquid in which the gas is to be dissolved. The space between the tube A and the wide tube DE acts as a safetyvalve if the pressure accumulates through the too rapid generation of the gas, or if a stoppage occurs in the delivery-tube, the liquid in the bottle is first blown out through this space, and the pressure is thus relieved.

FIG. 224.

A

FIG. 225.

Fig. 225 shows a very convenient little apparatus for generating and washing small quantities of gases, for testing, or other purposes: the wash-bottle is made from a homœopathic vial, rubber corks being used, and the bent tubes by bending ordinary glass tubing over a flame as described on page 143. The funnel-tube permits the addition of fresh liquid to hasten or continue the action as the operation progresses. It is usual to add merely sufficient water to cover the orifice of the delivery-tube in the wash-liquid at the beginning of an operation, as the aqueous vapor carried over by the gas condenses in the wash-bottle, which soon increases in quantity, and may accumulate in a long operation to an extent which will necessitate a partial discharge of its contents or the entire cessation of the process. As the apparatus suitable for each operation must be especially selected, general observations on the solution of gases will not be so useful in this chapter as a detailed process in connection with each preparation where it is described in the subsequent pages. One general rule should be noted, however,-i.e., that gases are generally more rapidly and thoroughly absorbed by cold liquids than by hot ones: hence the receiving bottle should be kept surrounded by ice or otherwise refrigerated.

Wash-bottle.

B

Gas-generator.

QUESTIONS ON CHAPTER IX.

SOLUTION.

What is meant by solution?

solvent?

stance?

place?

What is the liquid used to make a solution called?

What is a saturated solution?

When is a substance said to be insoluble?

What two kinds of solution are there?

Give examples of each.

How may the solution of solids be facilitated?

What is the effect of dissolving a solid body specifically heavier than the

How may this be shown?

Is a saturated solution of one substance capable of dissolving some other sub

Give an example.

When solids dissolve rapidly in liquids without chemical action, what takes

How are freezing mixtures made?

What is the effect if during the solution chemical action takes place?

How are solutions usually made by the pharmacist?

What is meant by circulatory solution?

Name the principal solvents used in pharmacy.

What are some of the advantages of alcohol as a solvent of glycerin ?
For what substances is ether a good solvent?

What advantages has ether over chloroform?

What are objections to carbon disulphide as a solvent?

Upon what do the methods for making solutions of gases in liquids depend?
Where a gas is freely soluble in a liquid, how is a solution usually effected?
What is the arrangement of a Woulffe's bottle?

Are gases generally more rapidly and thoroughly dissolved by cold or hot liquids ?

CHAPTER X.

SEPARATION OF FLUIDS FROM SOLIDS.

THE operations involved under this head are among those which are most frequently used in pharmacy,-i.e., Lotion, Decantation, Colation, Filtration, Clarification, Expression, Percolation, etc.,—and the principles which govern the successful performance of these practical processes should be mastered early in the career of the student. They are almost exclusively mechanical processes.

FIG. 226.

Lotion, or Displacement Washing, is the process of separating soluble matter from a solid by pouring a liquid upon it which will dissolve and wash out the soluble portion. The separation of the fluid from the solid is generally effected by placing an obstruction in a funnel or cylindrical vessel, such as a plug of cotton or tow, notched cork, filter-paper, etc., and then, having introduced the solid into the funnel and arranged a suitable vessel beneath, the liquid is poured upon it. (See Percolation.) Precipitates are frequently purified from contaminating soluble matter in this way. A very convenient method of applying the liquid is by the use of the spritz bottle (see Fig. 226). This is usually made from a flask, but a round-shouldered pint bottle of the diameter most easily grasped by the hand is preferable. Two glass tubes, one bent at an acute angle and the other at an obtuse angle, are used; one end of the former is drawn out to a capillary orifice, and the other extends nearly to the bottom of the bottle. The obtuse-angled tube merely enters the bottle below the cork; the upper portion of this tube should be held in the gas-flame, so as to fuse the edges of the glass and thus prevent cutting the lips when it is used. By filling the bottle with liquid, and blowing with the mouth through the tube, a stream of liquid is ejected from the capillary orifice which can be directed to any portion of a solid substance that is to be washed. It is often desirable, in order to save time, to use the liquid hot. One of the wicker-covered bottles in which Farina cologne is imported answers a good purpose here to prevent burning the fingers, and if care is used to pour in a small quantity of hot liquid first and agitate it before adding the rest, so that the glass may be gradually warmed, there is no danger of fracturing the bottle.

Spritz bottle.

Continuous Washing.-The use of the spritz bottle for small operations is convenient. A simple method of automatically supplying the wash-liquid in larger quantities is shown in Fig. 228. This requires

no attention from the operator except at the beginning of the operation. The bottle is furnished with a perforated cork and a short glass tube. All that is necessary is to fill the bottle and adjust it over the funnel so that the end of the tube shall be at the height desired for the liquid: on tilting the bottle slightly (if the tube selected is not too narrow in diameter) the liquid will run out into the funnel until it rises to the orifice of the tube, when the flow will cease. As the liquid gradually passes through the solid substance in the funnel, the level falls, and bubbles of air pass through the tube into the bottle, the liquid once more flows, and the operation continues until the bottle is empty. Many elaborate methods of continuous washing have been suggested, and many have been practically tried by the author, but if care is taken in the simple apparatus just described to have the tube of proper diameter, at least so wide that the force of capillary attraction shall not be strong enough to prevent the ingress of air, it is the most satisfactory of all. Bottles having narrow mouths may often be used in

FIG. 228.

the same way, and the cork and tube be dispensed with. A little practice will enable the operator to make a bottle in which the parts are adjusted to a nicety. On the large scale, Prof.

B. S. Proctor's suggestion of two carboys may be used,-one above and inverted, containing the liquid, supported by a box having a circular hole cut in its side, and the other inside the box, containing the funnel and filter.