Dispensing by Drops.


Other tomes: AJP1883


Abstract from an Inaugural Essay.

The size of a drop generally depends upon and is influenced by at least four conditions. (See also paper by Prof. C. F. Himes, in "Amer. Jour, Pharm.," p. 394, 1883.—EDITOR.)

First: the self-attraction that the particles of liquids have for each other.
Second: its adhesion to the matter on which it is formed.
Third: the shape of this matter.
Fourth: the physical relations existing between the matter on which it is formed, the liquid constituting the drop itself, and the medium through which it passes.

In my experiments I have found that the greatest variance is caused by the third condition, viz.: the shape of the matter, to which may be added the amount of surface, as it is obvious that the more surface the greater will be the adhesion, and therefore will require more liquid to overcome tills force, and consequently will produce a larger drop. This is practically illustrated below, when, in dropping from a glass stopper the surface from which the liquid has been dropped has a U-shape and is formed on the convex side, while from a minim measure it is dropped from the concave side of a V-shaped surface, giving the drop only a very small point to form on, and therefore must be much smaller. This is further illustrated in dropping from a glass stopper held at different angles. When held horizontally the drop is about twice the size of one dropped at an angle of 45 degrees. The difference is still greater when a common cork is taken, as it has a more acute angle. In the case of tincture of opium, the drop from a common cork, when held in a horizontal position, was more than twice as large as when held at an angle of 45 degrees.

Another very important feature in the matter of dropping is the rapidity with which it is done. It is a well-known fact that the less the interval between successive drops, the larger they will be. This interval has been called the growing time, and it follows that if this growing time is constant in the same liquid, the size of the drop will be the same.

It has been shown by actual experiments, that when the growing time is decreased below 0.333 second (coconut oil was used in this instance) a continuous stream was the result, but of course the density of the liquid regulates this to a certain extent. It is also a curious fact that a stream so produced, delivers less in a given time than a series of large drops.

This rapidity of dropping is one of the greatest obstacles to overcome, for very few pharmacists will drop the same liquid in the same time, and if laws are to be laid down, governing dropping, the time certainly claims a large share of attention, for the same mistake is just as likely if not more so, to happen in this instance than in the previous one, for a pharmacist who dispenses 100 drops of a liquid at the rate of three drops a second, will give one half as much again as another who measures the same liquid at the rate of a drop every second and one half.

Prof. Guthrie has shown the effect of gradually decreasing the strength of saline solutions. Dropping, at the rate of two seconds, he found that decrease of solid constituents produced precisely the same effect upon the size of the drops, as a decrease in the growth rate in the drops of homogenous liquids. I find that these facts, however, have their greatest importance from a theoretical point of view, practically there is very little, if any, difference, although in some instances it does seem as though the matter in solution might be the cause of the decrease in size by increasing its specific gravity. The following table gives the result of my experiments, having chosen the glass stopper, minim measure and lip of the bottle in which the liquids are ordinarily kept, to drop from.

By comparing my table with those of Prof. Procter or Mr. Durand, it will be noticed, in a number of instances, that they vary very widely, about the only way I can account for this is, that the lip of the minim measure, which I used, must have been much smaller than theirs, but even when the same vessels are used, there is such a variety of results, that to get a medium size an average is required to be taken. This I have done in all of the unimportant liquids. How greatly they vary may be seen in the case of Acetum opii; in the first trial the result was 120 drops to a drachm, the second 85, and the third 103.

There are still other conditions which yield more or less influence on the size, and one which deserves mention, is the angle at which the vessel is held. I have already shown that a cork may be held so a drop can be obtained twice as large as another where the cork has been held at a different angle, the same is true with a bottle, but not quite in so great a degree.

The fulness of the bottle also exerts some influence, as tincture of aconite, when dropped from an ounce vial full, yielded 110 drops to the drachm, but when only one-fourth full gave 116 drops, also liquor potassii arsenitis, from a full ounce vial, gave 66 drops, and when one-third full, only 57. In the one case, decrease in the amount of liquid decreased the size, while in the other it was increased. The drop from an ounce vial was in most instances the same as from the shop bottle.

By a careful perusal of the above we can readily notice that the different classes of preparations can be grouped together, as for instance, the tinctures or alcoholic preparations may be classed as a group, whose drops are about one half the size of the aqueous liquids, while the oils and acids form an intermediate group between the two. Durand must have taken notice of this fact, when he laid down his two general rules concerning drops as follows:

First: that liquids, with a small proportion of water, afford a small drop, and vice versa.
Second: that amongst liquids containing a large proportion of water, those not charged with remedial substances, give a larger drop than those same liquids having extraneous bodies in solution.

In summing up my labors on this subject, there is only one general conclusion that I will mention, as it covers all of the others, and if properly heeded may be the means of saving considerable trouble, and I might say is also in harmony with those who before me have given the subject a still more thorough investigation. Having shown that the same liquid under different and even the same circumstances, varies in dropping so much, that no reliance whatever can be placed in this method of dispensing medicines, therefore their administration in this form is always attended with more or less danger.

Preparation. Shop bottle. Glass stopper. Minim measure.
Acetum Lobeliae 51 48 64
Acetum Opii 66 57 65
Acetum Sanguinariae 102 92 92
Acid. Acetic 82 49 101
Acid. Acetic Dilute 94 55 99
Acid. Carbolic 82 66 110
Acid. Hydrobromic 57 65 70
Acid. Hydrochloric 60 57 96
Acid. Hydrochloric Dilute 70 51 62
Acid. Nitric 82 66 124
Acid. Nitric Dilute 63 60 81
Acid. Nitrohydrochloric 87 74 92
Acid. Nitrohydrochloric Dilute 58 54 62
Acid. Phosphoric. 54 43 62
Acid Sulphuric 160 152 172
Acid Sulphuric Dilute 57 47 60
Acid Sulph. Arom. 97 94 144
Aqua Ammoniae 45 41 54
Aqua Destillata 64 ... 61
Liquor Potass. Arsen 58 61 77
Oleum Anisi 76 73 112
Oleum Amygdalae Am. 102 77 125
Oleum Cari 108 84 133
Oleum Chenopodii 94 75 129
Oleum Caryophylli 98 75 133
Oleum Cinnamomi 77 73 112
Oleum Crotonis 84 62 104
Oleum Cubebae 86 80 120
Oleum Gaultheriae 93 93 136
Oleum Hedeomae 95 83 130
Oleum Lavandulae 105 78 133
Oleum Monardae 82 76 125
Oleum Menthae Pip 88 73 132
Oleum Menthae Viridis 95 81 132
Oleum Myristicae 98 83 128
Oleum Origani 91 83 133
Oleum Pimentae 102 86 133
Oleum Rosmarini 92 88 133
Oleum Sassafras 83 77 142
Oleum Tanaceti 110 91 136
Oleum Terebinthinae 103 90 142
Spiritus Ammon. Ar. 108 87 139
Spiritus Camphorae 98 79 140
Spiritus Aether. Comp. 120 88 140
Spiritus Aether. Nit. 88 86 144
Spiritus Menthae Pip. 98 86 143
Syrupus Scillae Comp. 106 87 122
Tinctura Aconiti 120 102 164
Tinctura Asafoetidae 102 85 145
Tinctura Belladonnae 94 81 128
Tinctura Benzoini Co. 98 81 146
Tinctura Cannabis Ind. 124 120 98
Tinctura Cantharidis 118 97 136
Tinctura Capsici 116 88 143
Tinctura Colchici 86 80 124
Tinctura Digitalis 114 79 145
Tinctura Ferri Chlor. 108 ... 139
Tinctura Hyoscyami 114 91 147
Tinctura Ignatiae 112 83 140
Tinctura Iodi 112 97 144
Tinctura Kino 116 100 148
Tinctura Krameriae 117 96 150
Tinctura Lavand. Co. 97 86 141
Tinctura Lobeliae 110 79 138
Tinctura Myrrhae 100 93 145
Tinctura Nucis Vomicae 112 105 148
Tinctura Opii 98 92 143
Tinctura Opii Camph. 94 86 135
Tinctura Opii Deodor. 109 89 141
Tinctura Rhei 98 82 144
Tinctura Sanguinariae 110 88 134
Tinctura Serpentariae 98 89 146
Tinctura Stramonii 100 93 120
Tinctura Tolutana 120 97 156
Tinctura Veratri Virid. 108 98 152
Vinum Aloes 71 54 94
Vinum Colchici Rad. 92 72 95
Vinum Colchici Sem. 86 71 105
Vinum Ergotae 148 99 122
Vinum Opii 96 72 102

The American Journal of Pharmacy, Vol. 56, 1884, was edited by John M. Maisch.