A treatise on pharmacy for students and pharmacists / by Charles Caspari, Jr.

  • Caspari, Charles, 1850-1917.
Date:
1895
    low denominations, as they can be made of larger size and^ con- sequently be more conveniently handled than heavier brass weights. Metric weights are made of iron, brass, or aluminum, in the same forms as already described for avoirdupois and apothecaries' weight. Fig. 14. Fig- 15. Aluminum wire weights. Aluminum grain weights. In connection with the operation of weighing, the term tare is frequently used to indicate the weight of the empty vessel (dish, box, bottle, or jar), in which the substance (liquid or dry) is to be weighed; gross weight is the combined weight of the substance and the container, net weight is the weight of the substance alone, Fig. 16. Set of metric prescription weights. (100 grammes to 1 centigramme.) obtained by subtracting, from the gross weight, the tare of the con- tainer. Instead of finding the exact weight of the container, the latter may be simply counterpoised or balanced by small shot or dry coarse sand contained in a suitable cup. Everyone who has occasion to use fine balances should early accustom himself to certain habits of care and neatness, which will materially preserve the sensitiveness of the instrument. The fol- lowing rules are recommended: Never allow the beam to oscillate when the balance is not in use. Immediately after the operation of weighing is completed, replace the weights in their proper receptacle and clean the pans with a soft towel. Never weigh deliquescent salts, or active chemicals, such as iodine, on the metal pans, but ahvays on glass,
    or in tared vessels. Ahoays weigh potent or poisonous drugs on stijf glazed paper, using two pieces of equal size to counterpoise each other. Never 'place large weights on the pans, or remove them, lohile the beam is in motion ; this is easily accomplished by means of levers for keeping the beam and pans at rest. Measures are vessels used lor determining the volume of liquids, and even dry substances; the latter kind do not concern the phar- macist, who is compelled, however, to have on hand a variety of vessels suitably provided with appropriate scales of measurement for liquids. Such vessels are usually made of glass and are known simply as graduates; they occur of different capacities from 1000 cubic centi- meters (1 liter) down to 5 cubic centimeters, and from 64 fluid- ounces down to 60 minims. The Phenix and Acme Graduates, manufactured in this country, are guaranteed to be accurate and made strictly according to the American standard of apothecaries' fluid measures; since Imperial measure differs materially from U. S. fluid measure, graduates made in England cannot be used in this country, unless they have been adjusted according to the American standard. Very accurate metric graduates are also now made in this country. Graduates of different shapes are in use, conical, tumbler- shape, and cylindrical (see Figs 17, 18, 19), the last named of which. Fig. 17. Fig. 18. Fig. 19. Conical graduate. Tumbler-shape graduate. Cylindrical graduate. although the most accurate, are but rarely seen in stores. Cylindri- cal graduates have a small diameter, which is uniform throughout the height of the vessel; hence errors in measurement due to capil- lary attraction are in these reduced to a minimum. For J and J oz. graduates the diameter is about J inch ; for 1 and 2 oz. sizes it should not exceed f inches; while for the 4 oz. size, IJ inch diameter
    Avill be ample. For measuring quantities less than two fluidounces the cone-shaped graduates will be found preferable to the tumbler- shape, 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 cylin- drical in form, of about the same diameter as tumbler-shape gradu- ates, and can be had for both metric and apothecaries' fluid measure. (See Figs. 20 and 21.) Fig. 20. Fig. 21. Metric fluid measure. U. S. fluid measure. Acme graduates. 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 measur- ing 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 meas- ured ; the mark to which the liquid is to be measured should be on a level Avith the operator's eye while the graduate is held in an upright position. Owing to capillary attraction, every liquid contained in a Fig. 22. Dr. Squibb's rainim pipettes. Dr. Curtman's cubic centimeter pipette. 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 inter- mediate 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 necessar}^, 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 Avhich 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 chlo- roform. Instead of being identical w^ith 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. Liquid. 120 minims Pheriix Graduate. 1 fluidounce Phenix Graduate. W. T. & Go's, exact Medi- cine Dropper. Pint or Quart Shelf Bottle. Distilled Water .... 48 46 128 Tincture of Aconite . 150 150 190 120 " " Belladonna . 144 144 174 108 " Chloride of Iron . 150 150 190 120 " " Opium . 130 130 154 " " " Camphorated 13() 136 170 " " Deodorized Opium . 90 110 124 80 Glycerin ... 90 76 90 Purified Chloroform . 234 240 304 160 " " second trial 274 279 360 180 Dil. Hydrocyanic Acid 60 80 75 60 bottle) For the administration of medicines certain familiar domestic measures are employed, which, although subject to considerable vari- ations, 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.