1900] MICROSCOPICAL JOURNAL 307 



The United States Pharmacopoeia directs that hydrar- 

 <:;ynun cum creta must not have the globules of mercury 

 visible under a microscope magnifying "foiir diameters." 

 With massa hydrargyri the requirement is "at least ten 

 diameters," and for unguentura hydrargyri "ten diame- 

 ters." I will pass around two samples of each prepara- 

 tion, one conforming to the pharmacopoeial requirement, 

 and one that does not. You see how easily the test is made. 



The approximate magnifying power of simple micro- 

 scopes with a single lens is easily determined sutiiciently 

 accurately for ordinary purposes. Focus the microscope 

 on some object and measure the distance of the lens from 

 the object. Divide ten by the number or fraction of an 

 inch, and the result will be the approximate number of di- 

 ameters which the microscope magnifies. As an example, 

 if the focal distance is two inches, the lens would mag- 

 nify ten divided by two, or. five diameters. One-half inch 

 distance between the lens and the object would give ten 

 divided by one-half, or twenty diameters. If a simple mi- 

 croscope consists of more than one lens, determine the 

 power of each, and add them together for the magnifying 

 power of the combined lenses. 



The leaves of senna and long buchu are frequently mis- 

 taken for each other by candidates before boards of phar- 

 macy. A simple microscope reveals the oil glands which 

 appear as bright spots in the buchu leaves, and are not 

 found in senna. The general resemblance of these leaves 

 and the difference shown by the microscope are illustra- 

 ted by the specimens before you. Short buchu and uva- 

 ursi are also sometimes confounded. Here the oil glands 

 in the buchu again distinguish the leaves from the uva- 

 ursi, as shown by the samples I pass around. 



Lupulin, of inferior quality, or when adulterated, is 

 easily detected by use of the compound microscope. I pass 

 one microscope with a specimen of pure lupulin, and an- 

 other showing the drug adulterated with sand. Powder- 



