LARD AND LARD ADULTERATIONS. 451 



best be found by experiment. It will differ with different samples, and with the time 

 of year, unless the temperature of the room in which the crystallization takes place 

 be artificially controlled. 



The crystals which have formed at the bottom of the test tube are taken out with a 

 piece of glass tubing, placed on a slide, covered with a cover glass, and examined 

 with a | or inch objective. Sometimes the mother-liquor will not be sufficiently con- 

 centrated to furnish a medium for the observation of the crystals, the evaporation of 

 the ether leaving them dry; in such cases the addition of a little cotton-seed oil will 

 be found advantageous. I did not find any advantage in washing the crystals ob- 

 tained with alcohol. I made a number of experiments in the crystallization from dif- 

 ferent solvents, alcohol, benzol, turpentine, chloroform, etc., but obtained often very 

 different crystals from the same fat crystallized from different solvents. 



On the theory that the crystals characteristic of beef fat are composed of stearine, 

 which would probably crystallize out before the other glycerides, if present, some of 

 the experimenters quoted above lay stress upon the examination of the first crystals 

 formed, with the idea that these would be the beef crystals. I have not found such 

 to be the case, the crystals formed when the solution had become concentrated being 

 generally like those first produced, except that they were not so perfect and distinct" 

 ive, having been more rapidly formed. Nor have I been able often to find such appear- 

 ances as are shown by Dr. Belfield's plates of mixtures of lard with 20 and 10 per cent, 

 of tallow, and which show the characteristic beef crystals among characteristic lard 

 crystals on the same slide. In only two or three cases did I find the two together on 

 the same field, and I am unable to show a single photograph of such a field, though 

 I endeavored to make such a slide. My experience has been that the kind of crys- 

 tallization first instituted predetermined the general form of all subsequent crystals. 



Slight differences in the temperature or in the concentration of the solution 

 when crystallization began seemed to have an influence upon the form of crystals 

 produced when the substance was a mixed fat, so that in some cases where no beef 

 crystals could be detected in a solution even by examining it at different periods, if 

 another solution were made and allowed to crystallize, beef crystals would appear. 



In Plates xxxi and xxxn are shown the characteristic crystals obtained from pure 

 lard* when crystallized from ether ; in Plate xxxvm the crystals from beef. From 

 these it will be seen that these fats, taken separately, give very different crystals. Just 

 what these distinctive crystals are is a most interesting question, both in a theoretical 

 and practical point of view. Some of the experts quoted above evidently thought, 

 from their testimony, that the lard crystal was palinitine, and the beef stearine. 

 Others seem to think they were both stearine modified and that this glyceride crys- 

 tallizes in different forms in the different fats. Whether these different crystals are 

 really composed of distinct glycerides, or whether they are mixtures of different but 

 definite proportions of the various glycerides found in fat, are questions that cannot 

 be answered in the present state of our knowledge. All we can say is that they are 

 quite different in appearance and that pure lard always gives the one, pure beef fat 

 the other form. Not only are the forms of the individual crystals different, but the 

 manner of aggregating themselves together is also quite distinct. 



This is seen from Figs. I and 2, Plate xxix, in which a small power 

 was used in order to show the manner of aggregation of the lard crys- 

 tals. They form feathery masses, radiating from a longitudinal axis, 

 with similar secondary branches. Thebeef fat crystals on the other hand, 

 us is shown in Plates xxvi and xxvin. from spherical masses radiating 

 from a common center, breaking up under the cover-glass into faii- 



* The lard ciystals make rather a difficult subject to photograph ; they are very thin 

 and the difference in transparency between them and the field is very little. The 

 slight refraction of light by their edges shows their outline on the plates, but only 

 a very delicate impression is made on account of the very thin edge." 



