356 Mr. C. Tomlinson on the Cohesion-Figures of Liquids, 



cohesion-figure on water, although of different chemical consti- 

 tution. Dr. Gladstone has has been so kind as to send me a 

 specimen of salicylate of methyle, €H 3 r € 7 H 5 3 , which gives a 

 figure somewhat resembling that of oil of lavender — arising, I 

 have no doubt, from a similar physical constitution. Cases of 

 this kind must be rare, and are not likely to interfere with the 

 application of cohesion-figures as a test. A much more serious 

 objection is the alteration which oils undergo by long keeping. 

 The specimens of oil of lavender, for example, which in 1861 

 gave the Carrigeen-moss-pattern figure, were so changed in 186^ 

 as to give only a plain film without any distinctive character. 

 On redistilling these oils, however, so as to get rid of oxidized 

 products, the distillate produced the lavender- oil pattern as it 

 did in 1861. 



On the other hand, the method is occasionally so delicate as 

 to excite the surprise of persons who have sought in vain for a 

 method of detecting differences in oils &c. which they largely 

 use in the course of their trade. For example, a manufacturer 

 informed me that it would be a great thing for him to be able 

 to detect the difference between beef-oleine and mutton-oleine. 

 The respective cohesion-figures of these substances show the dif- 

 ference plainly. Again, balsam copaibse is often adulterated 

 with castor oil, for the detection of which the usual tests are 

 either troublesome or inadequate. The method of cohesion- 

 figures detects the adulteration immediately. Again, olive oil 

 is frequently mixed with poppy oil, or sesame-seed oil ; not 

 only may these mixtures be detected by means of their cohesion- 

 figures, but also the relative proportions of the respective oils. 



Although for all practical purposes water would be used as 

 the adhesion surface in the production of these figures, consider- 

 able interest arises from noting changes undergone by the figures 

 when other surfaces are used. In my first paper, in 1861, it 

 was stated that wood-spirit on the surface of mercury gave a 

 very different figure from what it did on the surface of water; 

 and in my second paper (Phil. Mag. March 1862) I described 

 the cohesion-figures of w T ater, ether, and alcohol on the surface 

 of sulphuric acid, and also those of one or two essential oils on the 

 surface of acetic acid. I have lately obtained a large variety of 

 figures by experimenting on such adhesion surfaces as those of 

 cocoa-nut oil, castor oil, paraffin, spermaceti, white wax, olive 

 oil, lard, and sulphur. Of course the substances, such as pa- 

 raffin, wax, &c, which are solid at ordinary temperatures, were 

 melted for the purpose of these experiments. Too high a tem- 

 perature was found to be disadvantageous, on account of the ten- 

 dency of the drop to assume the spheroidal state. Lard is ad- 

 vantageous, on account of the length of time that it remains 



