Dr. Guy, on Microscopic Sublimates. 5 



placed the TiroTrtli of a grain of pure crystallized strycbuine 

 on a clean slab of white porcelain, in the centre of a glass 

 ring about an eighth of an inch thick, and with an opening 

 -y^ths of an inch wide. Over this ring I placed a disk of 

 window glass, the size of a shilling, quite clean, and dried 

 and warmed in the flame of the spirit-lamp. This simple 

 apparatus I supported on the ring of a retort-holder, and 

 placed before me at such a height that the glass disk was a 

 little below the level of the eye, so that I could catch the 

 reflection of the light from the surface of the disk, at the 

 same time that I could see through the glass the changes 

 taking place on the porcelain. I then applied a small flame 

 of a spirit-lamp to the part of the slab bearing the strych- 

 nine, beginning with the point of the flame barely reaching 

 the slab, and gradually approaching nearer and nearer, till I 

 perceived a mist on the glass disk. As soon as this happened 

 I withdrew the lamp, and found that a milk-white spot 

 formed in the centre of the mist, and speedily enlarged, till 

 it became a white circular stain about the sixth of an inch 

 wide. As the mist settled on the glass, the strychnine was 

 observed to darken. 



After an interval of about a minute, I removed the disk, 

 adjusted a second, and repeated the operation, with the same 

 result, only that the white spot was larger and the strychnine 

 darker. A third disk received a still larger sublimate, and 

 the strychnine melted into a brown layer. The melted alka- 

 loid, growing darker with each fresh operation, yielded six 

 more well-marked sublimates, and was then reduced to a 

 jet-black spot of carbon about the size of a split-pea. The 

 seventh spot was the largest, and was formed by several 

 small, white, circular spots, spreading and coalescing. 



In this instance, then, a thousandth of a grain of crystal- 

 lized strychnine yielded nine distinct sublimates in succes- 

 sion ; and among these there must have been more than one 

 weighing less than the ■, ^l o,-, th of a grain. 



Of these nine sublimates I took the third in order, sub- 

 mitted it to the heat of the spirit-lamp, and obtained from it 

 two distinct white sublimates, leaving on the disk itself a 

 stain which was not removed by the further application of 

 heat. Now, if I assume, what I think I am justified in 

 doing, that this third sublimate did not weigh more than the 

 -3-J^y^th of a grain, the smaller of the two (for they were of 

 unequal size) must have consisted of less than the , „ j, ^ ^ th of 

 a grain. 1 may add that from each of three or four succes- 

 sive -p-o-Jn^,ths of a grain (a quantity visible as a bright speck 

 on a slab of black glass) I have obtained a single well- 



