Solutions 



NITROCELLULOSE SECTIONS 



143 



in using other than a proprietary product, 

 is the fact that some nitrocelhilose mix- 

 tures are quite ^^olentl3' explosive when 

 dry, whereas both celloidin and Parlodion, 

 though they burn briskly if given the 

 opportunity, do not ignite with explosive 

 violence. Cellulose nitrates other than 

 those indicated under brand names are 

 always marketed in solution and should 

 never be stored in the dry state. Many of 

 the older books suggest that chips of nitro- 

 cellulose material, to be used for embed- 

 ding, be stored under water. This advice 

 is given not to lengthen the life of the 

 chips, but only to avoid the risk of 

 explosion. 



Celloidin, which term will be used 

 throughout the rest of this chapter when- 

 ever a nitrocellulose-embedding medium 

 is meant, is soluble in a great variety of 

 modern solvents, but most techniques are 

 based on its use in a solution of a mixture 

 of alcohol and ether. 



Preparation of Solutions 



Celloidin is not easily soluble in the al- 

 cohol-ether mixture usually employed, 

 therefore a special method must be used 

 to prepare the solutions. The chips of dried 

 material are first removed from the bottle 

 in which they have been kept and placed 

 in a desiccator overnight. The only real 

 enemy of the success of embedding in cel- 

 loidin is water, and at no stage in the pro- 

 ceedings may one risk contamination. It 

 ' is usual to carry in stock a 16% solution 

 of celloidin, therefore, 16 grams of these 

 dried chips should be weighed. These chips 

 are placed in a dry bottle fitted -with a 

 glass stopper which has been tested for fit. 

 Fifty parts of absolute alcohol are then 

 poured over them. If this alcohol is not 

 taken from an unopened new bottle, it is 

 desirable that it be carefully dehydrated 

 either with calcium sulfate or copper sul- 

 fate before being used for this purpose. 

 The bottle is left at room temperature 

 overnight, in order that the celloidin may 

 swell, and when this swelling is complete 

 50 parts of anhydrous ether are added. 

 The ordinary ether of commerce and the 

 ether used for anesthetic purposes are 

 worthless; one must employ the variety 

 sold as ether anhydrous by sodium. Any 



attempt on the part of the worker to re- 

 move water from commercial ether with 

 sodium in his own laboratory will produce 

 nothing but a serious explosion. The an- 

 hydrous ether should always be taken 

 from a freshly opened can. The bottle is 

 rotated slowly until the celloidin is com- 

 jiletely dispersed through the mass. The 

 selection of a solution of this strength is 

 based on the fact that it is about the thick- 

 est solution which may reasonably be 

 poured from a bottle. Not too much of the 

 material should be prepared at one time, 

 since ether always evaporates through 

 even the best fitting stopper. The only 

 method known to the writer of keeping the 

 material satisfactorily is to secure one of 

 the bottles, once common in pharmacies 

 but now difficult to obtain, in which the 

 ground glass stopper is itself covered with 

 a domed cap — like that on a balsam bottle 

 — ground to the neck. If such a bottle can 

 be obtained, the outer cap, but not the 

 inner, may be greased with glycerol and a 

 relatively ether-tight seal thus secured. 

 Under no circumstances should celloidin 

 solutions be stored in an icebox in the hope 

 of diminisliing the rate of evaporation. If 

 these cold solutions are then brought out 

 into a warm room, moisture will condense 

 all over the bottle and over the solution 

 as it is being poured. In Chapter 27 under 

 the heading E 22.1 will be found sugges- 

 tions for various other solutions which 

 have from time to time been made. 



Infiltration of Objects with Nitrocellu- 

 lose Solutions 



In the course of embedding in paraffin, 

 as described in the last chapter, it is just 

 possible to get away with slightly im- 

 perfect dehydration. In impregnation with 

 celloidin it is absolutely impossible. The 

 prime prerequisite to the successful infil- 

 tration of a specimen is that it be per- 

 fectly dehydrated. For this purpose the 

 specimen should be brought up in the con- 

 ventional manner through such series of 

 alcohols as may be necessary until abso- 

 lute alcohol is reached. It should continue 

 dehydration for some considerable time 

 in at least two changes of absolute alcohol, 

 the last of which has either been drawn 

 from a sealed bottle, or from a bottle in 



