SEPTEMBER 18, 1902] 
NATURE 
593 
action with water, into as much more sulphate along now with 
potassium amidosulphate, which latter substance contains all 
the nitrogen and twice as much hydrogen as belonged to the 
imidosulphate. Lastly, the amidosulphate interacting with 
water gives a third quantity of potassium sulphate, equal to the 
Jast, and also ammonia, having all the nitrogen of the nitrilo- 
sulphate started with, three times as much hydrogen as the 
imidosulphate, and nothing else. That is to say, the nitrilosul- 
phate and the ammonia have no other radical than the nitrogen 
the same, while three single interactions have been necessary to 
separate in this way the nitrogen radical from the three atoms 
of the potassiumsulphonyl radical. Therefore the nitrogen 
radical is tervalent and its quantity is the atom. Again, there 
are three atoms of the univalent hydrogen radical in the am- 
monia molecule, because in each of the three interactions an 
equal quantity of this radical is brought in from water. Am- 
monia shows only one pair of radicals, behaving, so far as its 
own interactions go, exclusively as acompound of amidogen and 
hydrogen, and these radicals are referred to as united or bound 
together in being ammonia. It is only the interactions of its 
derivatives, primary, secondary and tertiary, that are indicated” 
by treating the amidogen as ultimately nitrogen and two hy- 
drogen radicals. But this involves the consideration of all 
three hydrogens as bound to the nitrogen; and it becomes, 
therefore, of vital importance to bear in mind that the hydrogen 
radical, proper to the ammonia itself, is bound to a nitrogen 
radical which carries also bound to it two other hydrogen 
radicals. 
Chemical formulz still remain to be considered. They are 
symbolisations of deductions from experimentally ascertained 
facts, and are independent of the interpretation commonly 
given to them as referring to the minute differentiated structure 
of substances. A chemical equation expresses a chemical change 
quantitatively by means of chemical formule which are mole- 
cular. In a case of double decomposition, therefore, there are 
four formulz ; but when two or more such interactions are 
expressed in one equation, because they occur together, the 
formule of transition-substances do not appear, and then 
numerals before formulze tell the number of interactions in which 
separate molecules of the substance have taken part. A formula 
represents the relative interacting quantity or molecule of a 
substance, while the single symbols cbmposing it stand each 
for an atom of the radical of a certain simple substance as 
possessed by the substance formulated. The connecting lines 
and dots, and certain collocations of the symbols, indicate the 
association of the simple radicals as compound radicals in 
different interactions. 
What is symbolised by position formule, and indeed by the 
formula altogether, are the chemical activities and abilities of 
the substance and its derivatives, and their analogies with those 
of other substances. When not in interaction, a substance has 
no constitution and no formula. In is certainly not on any experi- 
mental grounds that it can be regarded as some spatial arrange- 
ment of unlike parts. To take the simplest case; if we start 
with sodium hydroxide and symbolise its molecule by some 
mark, such as X to begin with, the interaction of the substance 
with an acid leads us to replace the X by two symbols and a 
connecting mark. One of these will be Na for the sodium 
radical ; let the second be Z for the other radical, and let a dot 
or stroke be placed between the symbols to mark them as those 
ofa pair of radicals in interaction. In other interactions, such as 
that with melted potassium acetate, we find need for a new pair of 
symbols, one being H for the hydrogen radical, while the other 
may be (. But it is easy to decompose two molecules of 
sodium hydroxide in one operation into molecules of sodium, 
hydrogen and oxygen, from which fact we learn that Z is replace- 
able by the double symbol O-H, and Q by O-Na. Thus, Na-Z 
and H—( became equally Na-O-H, which records the ultimate 
radicals of sodium hydroxide, together with all its interactions, 
immediate and remote. But it does this with no more implica- 
tion of spatially placed and tied parts than is made by expressing 
the measured flow of time by a straight line, or than is to be 
found in @ seconds of time, or in ¢ as the third power of a 
number, unless we specifically condition this symbol as stereo- 
metric. A formula is not to be read—on experimental grounds, 
I mean—as a symbol of parts juxtaposed and joined on, and 
should be regarded as an intricate but legible monogram telling 
the chemical nature of the substance. Every symbol in it is to 
call to mind a phase of the chemical activity of the substance 
or of its derivatives, a phase that may be for the time as the 
NO. 1716, VOL. 66] 
substance itself to the investigator, just as a pigment substance 
becomes only a red or a white to the painter. For example, 
salt is often nothing more than its chlorine phase to the chemist 
when he wants only a soluble chloride; whether it is of 
potassium, sodium or ammonium, then, matters not to him. 
The double linking of the carbons in ethylene is a symbolised 
expression of facts without reference to hypothesis. The two 
carbon radicals of ethane or of alcohol behave together just as 
does the single carbon of methane or the nitrogen of ammonia 
in being, but with a valency of six, continued to other com- 
pounds devoid of all the other radicals of the ethane or alcohol 
—that is, of the hydroxyl and the hydrogens. The quadri- 
valency of each carbon is made up by the interaction necessary to 
dissociate or to bring together the two methyls, which counts 
as a unit of valency to each carbon. Ethyl hydrogen sulphate 
decomposes into sulphuric acid and ethylene, the hydrogen- 
sulphate radical with a hydrogen radical becomes the acid as 
the one product, while the methylene radicals again pair off as 
the two methyls had done when ethane was formed, thus pro- 
ducing the non-saturated substance, ethylene. Since there is a 
perchlorethylene, the second linking mark falls between the two 
carbons ; and when ethylene passes back to an ethane compound 
two units of valency are displayed by it without the carbons 
becoming dissociated. 
Position formule of isomerides, such as those of propyl 
alcohol and acetone, present no difficulty, because they are 
interpreted as the expressions of unlike double decompositions. 
It is not unfrequently the case that no constitutional or struc- 
tural formula can be given to a substance which shall express all 
the pairs of radicals possible in its interactions, of which the 
best-studied example is that of ethyl acetoacetate. This state 
of things, known as tautomery, admits of no other interpretation 
than that there are really two substances existent, of which one 
only is known, the other or so-called ‘‘ pseudoform ” requiring the 
assumption of its existence as a transition-substance only. The 
notion of the shifting hydrogen radical is but the hypothetical 
way of viewing the intervention of the intramolecular change 
by which the substance becomes its ‘‘ pseudoform.” 
The cyclic formula of benzene expresses the fact that, unlike a 
fatty hydrocarbon, benzene shows but one pair of interaction 
radicals, hydrogen and phenyl. The ‘‘ortho-,” ‘* meta-” and 
“*para-” positions in benzene derivatives are only expressions 
of facts of ‘‘ position” isomerism, such as those pertaining to 
other non-saturated compounds, but more complex to unravel 
and more varied and interesting. It is doubtful whether the 
Kekulé ring does not remain as efficient a symbol as any stereo- 
graphic substitute yet proposed for it; but it itself is purely a 
symbol of chemical interactions, and has no spatial significance 
other than what may be put into it by convention. ‘* Adjacent,” 
“* opposite ” and the like have only application literally to the 
arrangement of the symbols ; but if the symbolisation is perfect 
the ‘‘ opposite” carbons will, as a matter of course, always 
indicate the same point concerning the chemical interactions. 
Whether the chemical formulze for the lactic acids are better 
arranged in a plane or as a tetrahedron is to be decided by the 
facts concerning these and other asymmetric carbon compounds, 
the object being to symbolise or formulate as distinct and comple- 
mentary in certain physical properties, but alike in their chemi- 
cal interactions, two isometric substances, simultaneously formed 
in molecular quantities. Enantiomorphous arrangements of the 
respective formulze of dextro- and levo-lactic acids fully meet 
the case, but the facts are in no way explained by these formule. 
In the enantiomorphously related hemihedral crystals of the 
corresponding salts of the dextro- and laevo-acids, and in their 
opposite rotatory effect in solution upon the plane of polarised 
light, we recognise something like a torsioned state of the whole 
homogeneous substance, something to be accounted for by 
peculiarity of chemical origin, but not something made more 
intelligible by any imagined arrangement of unlike parts. It is 
possible to give an account of the chemical facts without making 
reference to mechanical structure, and then to reason about 
them somewhat in the following way: Given the case of a sub- 
stance doubly equipped with the power to take part in a certain 
interaction, and considering that the exercise of the power can 
only be single, and that it cannot be made without affecting and 
transforming, or perhaps nullifying, the second equipment with 
power, predict what will happen. That is the prediction called 
for concerning any interaction which generates an asymmetric 
carbon compound. The result could never have been predicted ; 
yet how natural and beautiful it is when it comes to us through 
