1866. | Hofmann and Modern Chemistry. 73 
in properties. In these researches we find the first germ of the 
theory of types which subsequently in the hands of Gerhardt, 
Williamson, and others assumed a more general form. 
We abstract some remarks from one of Dr. Hofmann’s papers* 
which bear strongly. on this point. At a very early period, as 
far back as 1837, Berzelius, on the grounds of Liebig’s researches, 
expressed the opinion that the natural alkaloids which at that 
period engrossed the undivided attention of chemists were peculiar 
ammonia compounds—conjugated compounds, in which the che- 
mical character of ammonia, modified indeed by its conjunct, was 
still perceptible. This view, which was principally founded on the 
remarkable analogy of the ammonia salts and the salts of the alka- 
loids, met by no means with general approbation when first started ; 
but it has been retained and carried out by Berzelius, and it cannot 
be denied that since that period, science has acquired a great 
number of facts which powerfully support his opinion. Organic 
Chemistry has been enriched by a long series of artificial bases, 
which is almost daily being increased. ‘These bases are formed in 
a variety of processes, many of which products we see generated by 
the direct action of ammonia on other compounds. Numerous ex- 
amples are given, and Dr. Hofmann remarks :—‘‘ From the transi- 
tion of these indifferent substances into bases under the influence of 
reagents, giving rise in so many cases to the formation of ammonia, 
does it not become exceedingly probable that in this case part of the 
nitrogen has been reconverted into ammonia, which uniting with 
the remaining elements has impressed its character on the whole 
compounds ?” 
To these investigations may be referred Gerhardt’s classification. 
Mr. G. C. Foster says, “ The reconciling of the theory of types with 
the theory of compound radicals, which resulted from the discovery 
of the compound ammonias by Wurtz and Hofmann, and the dis- 
covery of the mixed ethers (or ethers containing two distinct alcohol 
radicals) by Williamson, prepared the way for Gerhardt’s classifica- 
tion of chemical substances, according to the types of double decom- 
position.” 
It must not be forgotten that in the memoir published in the 
‘Philosophical Transactions’ already referred to, will be found the 
first typically written formule. Researches of this high character 
leading to such important results in the philosophy of a science 
could not fail to earn for their author substantial acknowledgments. 
The interest taken by the Royal Society was evinced by two succes- 
sive grants of large sums of money during the progress, and to 
* «On the Action of Chloride, Bromide, and Iodide of Cyanogen on Aniline,’ 
‘ Quarterly Journal of the Chemical Society,’ vol. i., p. 285. 
+ ‘British Association Report: 29th Meeting at Aberdeen, 1859,’ p.1. This 
report is deserving of careful study. 
