The Molecular Volume of Solids. 



465 



Mnf, and the silicic acid the same volume constitution as quartz, viz., 

 SiJOJ, thus :— 



Tephroite=Mn*Si*0*=9 xH=48^ obs. vol. =48-6. 

 Faisbergite^Mn]Ca 1 1 S^ O 1 1 ^32x5 : 52=176-64 obs. vol. = 176-64 . 



In the first of these minerals the oxygen stere dominates, whilst in 

 the latter it is the manganese stere. 



Hermann, examining a series of oxides having the form RO, finds 

 that the volume of the oxygen in them=5, which he designates as its 

 normal value. The volume (5) is probably correct, but why this par- 

 ticular volume should be dignified by the term normal, it is not so 

 easy to see. The volume of a monatomic molecule of oxygen is the 

 only one entitled to be called normal if it could be got at, and is 

 probably =20. He then infers that the specific gravity of solid 

 oxygen is - 1 -g 6 = 3*2. It is unnecessary to speculate on what is the 

 specific gravity of solid oxygen, but it may be remarked, in passing, 

 that solid oxygen cannot have less than two atoms in its molecule, 

 and that its molecular volume is probably 20, which would give 

 1^=1-6 as its probable specific gravity. Hermann then proceeds to 

 assign this volume (5) to the oxygen of water, H 3 0, the molecular 

 volume of which=18, and then deducting (5) from (18) he obtains 

 13 for the volumes of the two hydrogen and 6' 5 for a single atom of 

 hydrogen. It is submitted that the tables which accompany this paper 

 contain abundant evidence that oxygen contributes (10) to the molecular 

 volume of water, and the hydrogen atoms (4) each. For in nearly a 

 hundred compounds containing hydrogen, the hydrogen atom is never 

 found with a volume greater than (4), but in a great number of cases 

 with that volume. The next step is to determine the volume of 

 nitrogen from a consideration of the density of fluid ammonia which is 

 taken as '629. Dividing the molecular weight of ammonia (17) by 

 •629 gives (27) as its molecular volume. Then deducting from (27) 

 3x6'5 for the three hydrogen atoms, leaves 7'5 for the volume of 

 nitrogen. The same observation may be applied to this determination 

 as to the previous one, that hydrogen never has so great a volume 

 as 6'5. According to the system of this paper, the molecular volume 

 of ammonia is 24 — Loschmidt makes it 23*5 — the nitrogen contri- 

 buting 12 and the three atoms of hydrogen (4) each, and therefore, 

 though the density of liquid ammonia may be '629 at a certain tem- 

 perature, the probable specific gravity of solid ammonia is ±%='708. 

 The density of liquid ammonia at — 10 o- 7 C. has been found to be as 

 high as '650. By such methods as the above, and others, Hermann 

 determines the normal volumes of the elements, but he supposes the 

 non-metallic elements and the lighter metals capable of assuming 

 other volumes than the normal ones in their compounds, though not so 



