CHARLES L. BRISTOL. 219 
flame so as to cover theglass. Aftera few trials suc- 
cess will be easy, save in the cases of some of the 
more infusible substances. These films may then be 
used in the spectroscope or for projection. A com- 
parison of Table No. 1 with Table No. 2 will indicate 
the prominent differences, and show the analogy between 
the iodides formed by the wet method and those by 
the dry. 
Table No. 8 shows the differentiation of the coatings 
by the use of ammonium hydrate and ammonium sul- 
phide. In differentiating similar coatings, ammonium 
hydrate and ammonium sulphide are used. They are 
most conveniently applied from a small wash-bottle 
containing the reagent, and having the mouth tube dip- 
ping under the liquid and the exit tube cut off close be- 
low the cork. Their action may be somewhat hastened 
by breathing. lodine itself gives a fugitive brown coat- 
ing that disappears rapidly, and must not be mistaken 
for a metallic coating. White coatings are rendered 
visible on the plaster of Paris tablet by coating it with 
lampblack. This furnishes a surface superior to char- 
coal and extends the value of the plaster tablet. 
Table No. 4 shows an interesting and suggestive fea- 
ture of these coatings and one worthy of thought. It is 
the relation of color to the atomic weight of the sub- 
stances when they are arranged according to Mendele- 
jeff s system. 
TABLE NO: 1. 
COLOR OF IODIDES FORMED IN THE WET METHOD. 
(Roscoe and Schorlemmer. ) 
Pb L— When a solution of a lead salt is mixed with a 
soluble iodide, a yellow precipitate is formed of Pb I,, 
which separates into yellow laminz. ‘On heating, 
this becomes reddish yellow, then light red, and lastly 
brownish black. 
108 
