Preparation of Mulls of Rubbery Materials for Infrared Examination. R. E. Rippere, Chemical Division, General Electric Co., Pittsfield, Mass.
rr
grinding of a sample of crystalline or friable material . . with Nujol or similar medium in a mortar into a fine paste for mounting hetween sodium chloride plates for infrared examination is usually satisfactory. Ho\vever, trouble is sometimes encountered with rubbery or t,ackygel materials, xThich frequently ball up on dry grinding or slip out from under the pestle n.hen the S u j o l is added. In this laboratory, satisfactory mulls have been obtained by first grinding the gel with an approximately equal volume of sodium chloride, until t,he gel has been disintegrated and earh p:irticle coated with salt crystals. Then the Nujol is gradually cvorked in and a uniformly dispersed slurry is obtained which is rcadily mounted between the sodium chloride plates of the Sample holder. This method is similar to that of macerating a biological specimen with sand for extraction. It has advantages over freezing the specimen, in that it can be used in humid weather without atmospheric moisture condensing on the chilled specimen and mortar. An occasional disadvantage of the freezing method is that the sample suddenly slips out of the mortar xhen pressure is applied to it with the pestle. HE
tvith molten C.P. fused zinc chloride. On immersing the sample in the tin bath with a quick motion, the smudge coalesces to form a light mass partly covering the tin. The sample is taken from the bare and clean surface of tin. It comes out with a bright coating of tin with no adherence of zinc chloride. The weight of tin in the coating is 5 to 10% of the weight of steel. The sample can then be stored for a felv days without further precaution until it can be analyzed. Tests of Coating Efficiency. To test the effectiveness of the tin coating, samples were cut from a mild steel rod of the following composition: carbon 0.25, manganese 0.43, aluminum
