70 MOUNTING AND LABELING. 



§ 164. Cleaning Mixtures for Glass. — The cleaning mixtures used 

 for cleaning slides and cover-glasses are those commonly used in chem- 

 ical laboratories : 



(A) Dichromate of Potash and Sulphuric Acid. 



Dichromate of potash (K 2 Cr 2 O,) 200 grams. 



Water, distilled or ordinary 1000 cc. 



Sulphuric acid (H 2 S0 4 ) 1000 cc. 



Dissolve the dichromate in the water by the aid of heat. Pour the 

 solution into a bottle that has been warmed. Add slowly and at inter- 

 vals the sulphuric acid. 



For making this mixture, ordinary water, commercial dichromate 

 and strong commercial sulphuric acid should be used. It is not neces- 

 sary to employ chemically pure materials. 



This is a very excellent cleaning mixture and is practically odorless. 

 It is exceedingly corrosive and must be kept in glass vessels. It may 

 be used more than once, but when the color changes markedly from 

 that seen in the fresh mixture it should be thrown away. 



(B) Sulphuric and Nitric Acid Mixture. 



Nitric acid (H NO s ) 200 cc. 



Sulphuric acid (H„ SOJ 3°° cc - 



The acids should be strong, but they need not be chemically pure. 

 The two acids are mixed slowly, and kept in a glass-stoppered bottle. 

 This is a more corrosive mixture than (A) and has the undesirable fea- 

 ture of giving off very stifling fumes, therefore it must be carefully 

 covered. It may be used several times. It acts more rapidly than the 

 dichromate mixture but on account of the fumes is not so well adapted 

 for general laboratories. 



MOUNTING, AND PERMANENT PREPARATION OF MICROSCOPICAL 



OBJECTS. 



§ 165. Mounting a microscopical object is so arranging it upon 



some suitable support (glass slide) and in some suitable mounting 

 medium that it may be satisfactorily studied with the microscope. 



Some objects are mounted dry or in air, others in some liquid misci- 

 ble with water, as glycerin, and still others in some resinous medium 

 like Canada balsam. Special methods of procedure are necessary in 

 order to mount objects successfully in each of these ways. The best 

 mounting medium and the best method of mounting in a given case 

 can only be determined by experiment, unless some previous observer 

 has already supplied the information. 



The cover-glass o?i a permanent preparation should always be consider- 

 ably larger than the object ; and where several objects are put tinder one 

 cover-glass it is false economy to crowd them too closely together. 



