will be ample. For measuring quantities less than two fluidounces the cone-shaped graduates will be found preferable to the tumblershape, but difficulty is often encountered in cleaning them properly, particularly the smaller sizes. The "Acme" graduates, introduced a few years ago, possess the advantage of being made flat on the bottom, without a foot, and hence are less liable to be upset or broken; they are admirably adapted for laboratory work, are cylindrical in form, of about the same diameter as tumbler-shape graduates, and can be had for both metric and apothecaries' fluid measure. (See Figs. 20 and 21.)

Duplex graduates, arranged for apothecaries' fluid measure on one side and metric fluid measure on the other, are not to be recommended, on account of the danger of confusion and the greater difficulty of accurate measurement.

Although minim graduates are extensively employed for measuring volumes of less than one-fourth fluidounce, it will be found more desirable to use minim pipettes (see Fig. 22) for quantities ranging from 5 to 60 minims; these instruments, first suggested by Dr. E. R. Squibb, are very accurately made and will be found extremely convenient. For measuring small metric volumes the graduated cubic centimeter pipettes of Dr. Curtman will be found very serviceable (see Fig. 23); they come in different sizes-5 and 10 and 25 Cc. capacity-each cubic centimeter being divided into tenths, and are especially adapted to pharmacopoeial testing.

As to the proper manner of holding a graduate while measuring liquids, it may be said that the firmest hold is obtained by grasping the graduate with the left hand in such a manner that the first or index finger encircles the lower part of the vessel, the thumb resting on the base and the second finger forming a support by being placed under the base; this leaves the third and fourth fingers free to remove

and hold the stopper of a bottle from which any liquid is to be measured; the mark to which the liquid is to be measured should be on a level with the operator's eye while the graduate is held in an upright position. Owing to capillary attraction, every liquid contained in a

graduate will present two concave surfaces, neither of which can be taken as the true level; hence a correct reading of the graduation can only be had by fixing the desired marking of the scale intermediate between the upper and lower edges of the liquid.

Graduates which have the same scale marked on both sides, or which are encircled by the markings of the scale, admit of more

accurate measurements and do not require that careful attention to levelling the graduate necessary with the plainer varieties.

Glass graduates are best cleaned by washing with a mop, using soap and water if necessary, rinsing with clear water and allowing the graduate to drain, either on a perforated tray or by hanging in a rack, but never should a towel be used to dry the graduate, as it is apt to leave lint adhering to the glass.

APPROXIMATE MEASUREMENTS. Owing to the varied density of liquids, the number of drops contained in a certain volume must vary greatly with different liquids; moreover the size of a drop is influenced by the size and shape of the vessel from which the drop is allowed to fall-so that a drop is a very uncertain quantity in the division of doses of medicines. The variability of adhesion to glass exhibited by different liquids as well as the rapidity with which liquids are allowed to flow from vessels, are other factors which determine the size of drops, as is shown in the case of chloroform.

Instead of being identical with the minim, drops may vary from one-fifth to one and one-fourth minim.

For the purpose of better illustration, the following short table has been inserted, showing the great variability in size of drops of different liquids:

TABLE SHOWING THE NUMBER OF DROPS TO A FLUIDRACHM.

For the administration of medicines certain familiar domestic measures are employed, which, although subject to considerable variations, are usually estimated as having the following capacity:

A teaspoonful, equal to one fluidrachm;

A dessertspoonful, equal to two fluidrachms;
A tablespoonful, equal to one-half fluidounce;
A wineglassful, equal to two fluidounces;
A teacupful, equal to four fluidounces; and
A tumblerful, equal to eight fluidounces.

Figs. 24, 25, and 26 represent convenient medicine glasses, well adapted for family use.

These vessels are now obtainable, accurately graduated and made to correspond to apothecaries' fluid measure-hence they are preferable to the variable tea-, dessert- and tablespoons generally met with, and should be employed altogether in the sick-room.

CHAPTER III.

SPECIFIC GRAVITY.

A KNOWLEDGE of the subject of specific gravity is of importance to the pharmacist, as it frequently enables him to detect impurities or to determine the identity and quality of the drugs he handles. Specific gravity means relative weight, or the relation between the volume and weight of bodies as compared with a standard-the standard for liquids and solids being distilled water, while atmospheric air or hydrogen is used for gaseous bodies; in other words, specific gravity is the ratio between the weight of any gaseous, liquid, or solid body and that of an equal volume of the respective standard. The principle of specific gravity was first announced by Archimedes, a Greek philosopher, who formulated the law that all bodies immersed in a liquid are buoyed up with a force equal to the weight of the liquid displaced by them; hence a piece of metal of the size of one cubic inch, when immersed in water, will exert as much less pressure on the bottom of the container as will equal the weight of one cubic inch of water-or a fraction over 252 grains. Floating bodies always displace their own weight of water, irrespective of their volume, while immersed bodies always displace their own volume of water, irrespective of their weight; hence all bodies whose volume weighs less than an equal volume of water are sure to float, only so much of the body being immersed as equals a like weight of water, while all bodies whose volume weighs more than an equal volume of water must sink and be completely immersed, as this downward pressure of the body exceeds the upward pressure or buoyant force of an equal volume of water.

As the volume of all bodies varies with temperature, it is essential that the comparison of weights be made at some fixed temperature and that equal volumes of the standard and body examined be weighed at the same temperature. In some countries the temperature of 4° C. (39.2° F.), at which pure water assumes its greatest density, is taken for the comparison of weights, while in the United States and German Pharmacopoeias, 15° C. (59° F.) has been fixed, with very few exceptions, as the normal temperature; the British Pharmacopoeia has selected 15.6° C. (60° F.). As the comparison of weight of equal volumes of bodies may be made at any temperature desired or convenient, and as the specific gravity will vary accordingly, it is necessary to state the temperature in connection with specific gravity; for instance, to say that a liquid has the