Bulletin of Pharmacy, vol. 9, no. 10, page 461-462, (October 1895).
Weight of Drops of Various LIQUID MEDICAMENTS.
Frederich Eschbaum has recently made an exhaustive study of the question propounded at the meeting of the German Pharmaceutical Association last year: “Is it possible to obtain from the same liquid, at all times, drops of identical size and weight?” The study is published in full in the Deutsche Medicinische Wochenschaft, from which we extract the following conclusions:
The size and weight of a drop are determined by two circumstances or conditions, viz.: (1) the adhesion existing between the liquid and the glass, and (2) the specific cohesion of the liquid.
In regard to the first condition, the author says: "Drops of uniform size cannot be obtained by uniformity in the size or shape of the neck of the container, since the quantity of liquid in the latter has an influence on the quantity massing itself into the drop. They can be obtained, however, from a burette, and the sharper the point of the latter the smaller the size of the drops; but it is the size of the external circumference of the point of exit which determines the size of the drop.”*
* Quicksilver is the only fluid that forms an exception to this rule. The size of the drops of this substance is determined by the diameter of the opening in the clear.
To demonstrate this proposition, Eschbaum gives the following figures:
of Point of Pipette
|Weight of a Drop|
|0.67 Mm||0.0134 Gm.|
SPECIFIC COHESION OF THE LIQUID.
The specific cohesion of various liquids varies within wide bounds, being greatest in water and least in ether, glycerin, and alcohol. To illustrate this, Eschbaum let the liquids drop from a burette of 6.56 Mm. external diameter at 15°C., and found that fifty drops of each named liquid had the following weight:
|Alcohol, dilute, G.P.||1.87|
The specific cohesion of a fluid is affected by temperature, but, according to our author, in small amounts the variation from this cause is too small to be taken into account practically.
The specific cohesion of a solution of solid substance in a liquid is lower than that of the liquid.
The drops of a solution, all other circumstances being equal, are therefore smaller than those of the menstruum.
The specific cohesion of liquids is therefore in inverse ratio to their specific weight, so that the absolute weight of a drop of a salt solution, for instance, is almost identical with that of a drop of the original menstruum.
All these results demonstrate the absurdity of our present methods, and led Eschbaum to formulate the following proposition for
Rational Dosage by Drops
As a standard of unity, let a pipette be chosen having an external diameter of point of delivery of 6.56 Mm. Such a pipette delivers drops of distilled water weighing 10 centigrammes each, or 10 drops to the gramme; or, of a tincture made of dilute alcohol, 26 drops to the gramme.
While the ordinary medicine·dropper, with a gum bulb, seems to Eschbaum the most convenient for the patient, on account of its inaccuracy and the careless habits of the majority of nurses he advises a measuring apparatus for lay use, described as follows:
The Rational Medicine-Dropper
Take an ordinary medicine-glass, holding from 30 to 60 Cc., and fit it with a bored cork through which passes a strong glass tube from 2½ to 3 cm. long, the inner end of which is even with the lower surface of the cork, and the outer end projects, say a centimeter, from the top of the latter. The delivery point is not drawn to a point, but is so molten as to leave a very small opening in it, while the lower end of the tube is molten only sufficiently to remove the sharp edge—and even this may be omitted. The outer end should have a diameter of 7 to 7½ Mm. (.28 to .30 inch) and be nearly flat, or only slightly rounded at the edges.
The dropper thus formed should be not more than half-filled, and when it is desired to use it it should be grasped in the palm of the hand and turned upside down over the spoon or other receiver. The heat of the hand, expanding the residual air, will slowly drive out several drops, each of exactly the same size. A well made dropper of this sort may be turned upside down and left thus for several minutes without a drop escaping until the hand (or other external source of warmth) is applied.
While the use of the “drop” as a unit of measure in medicine and pharmacy is to be discouraged, and no one is more convinced of the fact than our author, he recognizes the impossibility of reforming the professions all at once, and the futility of such an attempt. He has therefore done the next best thing, and, with most commendable patience and accuracy, worked out a table of the weight of drops of the various medicaments in common use, selections from which we present below. The results presented in the following table were obtained by the use of a burette with aa external diameter of 6.56 Mm. (say .26 or a full quarter of an inch). It is unnecessary to remark that a burette should be firmly held in measuring, as a trembling hand causes the drop to be shaken off the point before it has completely formed.
|Acid, hydrochloric||11||Solution of formaldehyde||16|
|hydrochloric dilute||10||" iron subacetate||12|
|phosphoric||10||" iron sesquichloride||9|
|sulphuric aromatic||25||" potassium arsenite||15|
|sulphuric dilute||10||Syrup of iodide of iron||10|
|Amyene hydrate||31||Spirit (alcohol)||29|
|Amyl nitrate||33||(alcohol (dilute)||27|
|Bromine||17||Spirit of ether||31|
|Ether||41||Tinctures prepared with alcohol||29|
|Ether, acetic||30||Tinctures prepared with dilute alcohol||27|
|Ether, bromic||29||Tincture ethereal acetate of iron||26|
|Extracts, narcotic, dissolved,
according to solvent, which see
|17-20||" ethereal chloride of iron||30|
|Glycerin||13||" malate of iron||14|
|Oil of almonds||20||" iodine||29|
|" anise||20||" musk||21|
|" caraway||21||" opium (G.P.)||25|
|" clove||20||" rhubarb, aqueous||14|
|" cinnamon||21||" rhubarb, vinous||17|
|" croton||21||" strophanthus||26|
|" lemon||26||" nux vomica||26|
|" olive||21||valerian, etheric||30|
|" turpentine, rectified||27||Water of bitter almond||19|
|Solution of ammonia aromatic||11||Water of camphor, colchicum, ipecac, etc.||17|
|" ammonia caustic||11|
|" carbolic acid||18|
To the Doctor
In conclusion, Eschbaum gives the following very good advice to the physicians: Either regulate your doses after the information conveyed to you in this table, or, what is better, name the absolute weight or measure of the dose prescribed.
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Last revised: 3 September 2011.