1874.) - - Physics. 137 
towards the more refrangible end, and shade off gradually so as to look like 
pieces of moulding illuminated from the violet side of the spe@rum. No. 1 
in Fig. 7 will give an idea of this, as well as of the positions of the various 
bands. By turning the spectroscope obliquely on the bottle containing this 
salt, an absorption-band at 107 can be distinguished with ease, but none above 
this can be made out, and, as regards this matter, the strongest contrast exists 
between the uranic acetates and its double salts. By 
crushing a few grains to a fine powder, with a little Fic. 13. 
water, between slips of glass, we may observe the 
absorption-bands by transmitted light with facility, 
and get a spectrum of a curious character as regards 
the irregular spacing of its bands. No. 1 of Fig. 8 
will give a good idea of this. Another noteworthy 
point is the very strong general absorption, which 
almost obliterates details of the spectrum, and makes 
it impossible to recognise any bands above one at 
about 135. In solution this general absorption is 
increased, and the absorption-bands are blended so 
that little can be done in the way of measuring them. 
If we make a solution of the neutral acetate in water, 
and examine its absorption, we shall find a faint band 
at about 105, and some indication of one at about 117, 
but a very heavy general absorption over the entire 
region above the first-named band obliterating all 
variations of shade. The addition of a little acetic 
or other strong acid will, however (while destroying 
the fluorescence of the solution), clear up its absorption- 
spectrum in a remarkable manner, giving us such a 
one as is shown at No. 3 of Fig. 8, which we have 
reasons for regarding as the absorption-spectrum of 
the double acetate of uranium and water. 
Anhydrous Uranic Acetate, U203;C,H303.—If this 
normal uranic acetate is dried, at a temperature of 
100° C., for some hours, it becomes opaque, and of a 
lighter and purer yellow tint, and is found to yield a 
fluorescent-spectrum, the bands of which are like those 
of the normal salt, but are all displaced downward 
in the spetrum. No. 2 of Fig. 7 will show the 
arrangement of these bands. The brightness of the 
fluorescence is very much reduced, and the first and 
last bands could not be made out with the apparatus 
at present in use. By inclosing this substance in 
dry powder, between slips of glass, its absorption- 
spectrum was observed with transmitted light, and is 
shown at No. 2 of Fig. 8. The general absorption is 
greater in this than in the case of the normal uranic 
acetate. 
The Double Acetates—These bodies give spectra 
which, whilst differing remarkably from that of the 
single acetate of uranium, agree strikingly among 
themselves. The fluorescent spectrum of the sodio- 
acetate of uranium is a type of a perfect double acetate 
of spectrum. All the double acetates show their 
absorption spectra with very great ease. The 
arseniates appear peculiarly fixed and inflexible in the 
relations under review. The four compounds ex- 
amined exhibit but one spectrum of fluorescence and one of absorption. The 
charaéteristics of the former are seen in Fig. 9, No. 1, and those of the 
latter in Fig. 10, No. 1. The double carbonates of uranium fluoresce faintly, 
showing a chara¢ter like that of the less brilliant double acetates. See 
VOL, IV. (N. S.) s 
