the frequency with which their solutions contain foreign matter which re- 

 quires filtering out. Insoluble dry drugs if prescribed should be reduced 

 to a fine powder,mixed with some of the menstruum and added to the rest. 

 In many instances it is well to suspend insoluble drugs by the addition of 

 gum, mucilage or a viscid fluid such as syrup or glycerin. If the vehicle be 

 water or an aqueous fluid and there are oils, balsams or oleo-resins ordered 

 these should be emulsified before being added to the bottle. The remainder 

 of the menstruum is now added and the bottle corked. 



The dispensing of fluid medicines necessitates a more complete acquain- 

 tance with the subject of incompatibliity than is the case with any of the 

 other forms of extemporaneous prescriptions. 



All solids should be weighed and all fluids measured. 



Fluids must be poured from the back of the dispensing bottles so as 

 ^0 save the labels. 



Powders must be taken from their bottles with a long spatula. 



The physician dispensing his own prescriptions may facilitate his office 

 work by keeping many of the frequently used drugs prepared in concen- 

 trated solution. These are made by dissolving a known weight of the drug 

 in a sufficient quantity of the solvent to make a definite volume of the final 

 solution. For instance if eight drachms of Bromide of Potassium are 

 dissolved in the quantity of water required to make a solution measuring 

 four fluid ounces, each four fluid drachms of the latter will then contain 

 one drachm by weight of the Bromide. These are called dispensing 

 solutions and are quite different to the percentage solutions of the chemical 

 laboratory and to those of the Pharmacopoeia. Such salts as the Bromides, 

 Iron Tartarate, Magnesium Sulphate, Potassium Iodide, Chlorate and 

 Nitrate, may readily be kept in this form; Bicarbonates in solution are 

 liable to change as do many of the organic preparations such as Chloral. 

 Dispensing solutions should always be kept in the dark. Though the re- 

 sult is hardly so good as when the Pharmacopceial method is used, flavoured 

 syrups may often be prepared by adding to a Simple Syrup a liquor of the 

 flavour required. In many other cases concentrated liquors or extracts may 

 be obtained from the pharmaceutical houses which may be diluted so as 

 to approximate the official preparations. In some cases it is of advantage 

 to keep weighed out and wrapped as powders, the insoluble drugs in powder 

 form needed for such a mixture as Mistura Cretae. Infusions especially of 

 digitalis should always be freshly made. 



Percentage Solutions. The disadvantages of the Imperial System 

 are most clearly seen when dispensing this class of solutions. Absolute ex- 

 actitude cannot be attained. For dilute solutions (1-3%) of highly active 

 drugs, e.g. Strychnine, Atropin?, the following method is to be recom- 

 mended; 110 minims of water weigh 100 grains; therefore if a 2% so- 

 lution be required 2 grains are dissolved in 110 minims. The bulk of the 

 resulting solution is slightly greater than 110 min. and its weight exceeds 



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