100 grains, but for all practical purposes 1 min. will contain 2/100 grain. 

 If one ounce were required, the simplest procedure is to make 4*4 x 110 or 

 495 min. and throw away 15. When a more concentrated solution e.g. 

 an ounce of a 10% solution of a salt, is prescribed a somewhat more com- 

 plex procedure may best be followed, as it is impossible to estimate what 

 the specific gravity of the resulting fluid will be. The following 

 procedure is often pursued: There are 437 grains to the fluid ounce, 10% 

 of this is 43. If 43 gr. salt were dissolved in 394 min. the bulk would not 

 be 1 fl. oz., but it 50 gr salt were dissolved in 450 of water the bulk would 

 obviously exceed a fluid ounce and in consequence such a solution might 

 be made and the excess thrown away. Very frequently and with sufficient 

 accuracy for many physician's purposes, percentage solutions are not 

 made as above by weight but by weighing the solids and measuring the 

 liquids, one minim being then considered as weighing one grain; one ounce, 

 one fluid ounce. 



Emulsions. These are mixtures of resinous or oily substances with 

 water. They consist of minute particles of the active substance surrounded 

 with, kept apart, and in suspension by means of mucilage made from one of 

 the gums. Acacia or Tragacanth are commonly selected in the dispensary. 

 Perfect natural emulsions are to be seen in milk and in the yolk of egg. 



Of the resinous drugs Asafetida, Myrrh, Copaiba, Extract of Male 

 Fern, the Tinctures of Cannabis Indica, Tolu, the Compound Tinctures of 

 Guaiacum, and Benzoin, frequently require treatment, as do Cod-Liver 

 and Castor Oils, Turpentine and Camphor. In the case of the gum-resins 

 such as Asafetida which contains a good deal of gummy matter it is not ne- 

 cessary to add extraneous gum to obtain an emulsion, that which is part of 

 the drug being sufficient on trituration with water. 



Emulsions are prepared with the aid of a mortar and flat pestle. A 

 thick mucilage is first made and with constant stirring a portion of the drug 

 is added in small quantities until the emulsion is obtained, when the balance 

 is added alternately with the remaining water in successive portions until 

 the whole is emulsified. 



With oils a second method may be adopted, called the English Method. 

 Two or three parts by weight of Gum Acacia are triturated in a mortar 

 with eight parts of Oil until the gum is completely suspended. Then one and 

 a half parts of Water are added at once when a few revolutions of the pestle 

 will secure an emulsion. The balance of the Water is now to be added in 

 successive quantities until the whole is used. If the emulsion is not com- 

 pleted in the first stage of the process or the water is added too freely 

 the oil separates and the emulsion is said to ' ' crack " and cannot be restored. 



On the Dispensing of Pills. The prerequisite of a properly made 



pill is a proper pill mass. This should possess the following characters, 

 consistence, cohesiveness, and plasticity. Proper consistence is es- 



127 



