Infiltration and Embedding in Paraffin Wax 33 



is uniformly opatjuc, has a fine, even grain, and excellent cutting 

 properties. Transparency again develops with age. It seems that 

 desirable properties are inherent in good paraffin. The undesirable 

 properties of some paraffins can only be minimized by the method 

 of preparation, casting and storage. 



The tcxtvne and cutting properties of paraffin can be improved 

 by the addition of rubber and beeswax, and in some formulas, a hard 

 wax, such as ceresin wax. Hance's formula is recommended. Dissolve 

 20 g. of crude rubber in 100 g. of smoking hot paraffin. Cool and 

 cast into slabs like canning wax. Make up the following mixture: 



Paraffin 100 g. 



Rubber-paraffin mixture 4—5 g. 



Beeswax 1 g- 



Heat the mixture smoking hot, filter through paper, and allow to 

 cool until it begins to solidify before putting into the oven tank. 



Ceresin wax may be added to the above formula, 2 to 5% by weight. 

 Other hard waxes need further study as hardening agents. Com- 

 pounded rubber paraffins are available from biological supply firms. 

 Tissuemat and Parlax are two products having excellent properties. 

 Commercial rubber paraffin can be mixed with twice its weight of 

 low-priced hard paraffin, greatly improving the properties of the 

 latter. Consult the catalogues and compare descriptions and prices 

 of trade-marked and other embedding paraffin waxes. 



Apparatus 



OVENS FOR INFILTRATION 



A water-jacketed copper oven with thermostat-controlled electrical 

 heating is the most reliable type of oven. In an oven of this type, 

 a built-in removable copper tank makes a suitable container for the 

 supply of melted paraffin. The tank can be ecpiipped with a brass 

 petcock, but petcocks develop leakage after little wear. A more satis- 

 factory method is to dip out the paraffin with a spoon as needed. 

 Debris settles to the bottom of the tank, and the clear paraffin is 

 used from the top. An incubator oven with a reliable thermostat is 

 satisfactory for paraffin work, but the temperature in diflierent parts 

 of the oven is not the same and must be determined. In the latter 

 type of oven the supply of melted paraffin may be kept in a container 

 with removable cover and dipped out with a spoon kept hooked in 

 the container. If it is possible to have two ovens for infiltration, use 

 an inexpensive wooden incubator oven set for 35°C. for preliminary 



