686 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[Mar A 1, 1673. 
considers this to be a proof against the identity of the 
two substances. Soxhlet shows that this depends on the 
presence of fat-globules in the milk, and finds that alkali- 
albuminate, when emulsionised by fat, is likewise in¬ 
capable of filtration (or with difficulty) through such 
earthenware cells. 
Zahn also states that the casein of the milk can be 
precipitated by sodium carbonate, but that solutions of 
alkali-albuminate cannot. This, however, does not de¬ 
pend on any chemical difference between the two sub¬ 
stances, but on the fact that in the milk other substances 
are present. The precipitation of casein from milk may 
likewise be effected by caustic alkalis and sodium phos¬ 
phate, as well as by sodium carbonate. The cause of 
the precipitation is the formation of calcium phosphate, 
which carries down the albuminate mechanically in the 
form of a finely granular precipitate. If alkali-albumi¬ 
nate is treated with calcium chloride and emulsified with 
fat, a like precipitate is caused on the addition of sodium 
phosphate. The statement made by Hoppe-Seyler that 
alkali-albuminate does not, like casein, yield potassium 
sulphide when treated with caustic potash, Soxhlet finds 
to be incorrect. He obtained a distinct evolution of 
hydrogen sulphide on the addition of acetic acid to the 
mass resulting from the treatment of alkali-albuminate 
with concentrated caustic potash. 
Still, another difference is stated by Hoppe-Seyler to 
exist between casein and alkali-albuminate, namely, the 
specific rotation exerted by these two substances on a 
ray of polarised light. Soxhlet thinks that this is no 
sufficient ground for establishing a chemical difference 
between the two, because the specific rotation is liable to 
be greatly influenced by the presence of salts and by 
other conditions of the solutions. 
From these various considerations the author comes 
to the conclusion that casein and alkali-albuminate are 
identical in every respect. 
PROFESSOR TYNDALL ON LIGHT. * 
The series of lectures from which the following notes 
are taken was delivered by Professor Tyndall at the 
Cooper Institute, New York. At the commencement of the 
first lecture, he said that the favour with 'which his writ¬ 
ings have been received in America had led to his being 
invited to lecture in that country. Having been given to 
understand that experimental lectures would probably 
be preferred, he decided to meet the wish, so far as he 
could, by selecting and transporting such apparatus as 
was suitable for such lectures, and to take some single 
department of natural philosophy, and illustrate the 
growth of scientific knowledge under the guidance of 
experiment. In his first lecture, he would describe 
certain elementary phenomena ; then point out how the 
theoretic principles by which such phenomena are ex¬ 
plained take root and flourish in the human mind, and 
afterward apply these principles to the whole body of 
knowledge covered by the lectures. The science of 
optics lends itself to this mode of treatment, and on it, 
therefore, he purposed to draw for materials. He 
thought it best to begin with the few simple facts re¬ 
garding light which were known to the ancients, and to 
pass on from them in historic gradation to the more 
abstruse discoveries of modern science. 
All men’s notions of nature have some foundation in 
human, experience. This is the broad foundation on 
which intellectual structures ultimately rest. The no¬ 
tion of personal volition in nature had this basis. In 
the fury and the serenity of natural phenomena the 
savage saw the transcript of his own varying moods, and 
he accordingly ascribed these phenomena to beings of 
like passions with himself, but vastly transcending him 
in power. Thus the notion of causality—the assumption 
that natural t hings did not come of themselves, but had 
* Abstracted from a report in the New York Tribune. 
unseen antecedents—lay at the root of even the savage’s 
interpretation of nature. Out of this bias of the human 
mind to seek for the antecedents of phenomena all 
science has sprung. 
The first sciences were those of observation, when the 
matter of thought was provided by man’s environment, 
and he had no notion of creating it himself. The ap¬ 
parent motion of sun and stars first drew toward them 
the questionings of the intellect, and accordingly as¬ 
tronomy was the first science developed. Slowly, and 
with difficulty, the notion of natural forces took root in 
the mind, its seedling being the actual observation of 
electric and magnetic attractions. Slowly, and with 
difficulty, the science of mechanics had to grow out of 
this notion ; and slowly at last came the full application 
of mechanical principles to the motions of the heavenly 
bodies. We trace the progress of astronomy through 
Hipparchus and Ptolemy ; and after a long halt, through 
Copernicus, Galileo, Tycho Brahe, and Kepler; while 
from the high table-land of thought raised by these 
mighty men, Newton shoots upward like a dominant 
peak overlooking all others from his stupendous eleva¬ 
tion. 
But other objects than the motions of the stars at¬ 
tracted the attention of the ancient world. Light was a 
familiar phenomenon, and from the earliest times we 
find men’s minds busy with the attempt to render some 
account of it. But without experiment, which belongs 
to a later stage of scientific development, no progress could 
be made in this subject. The ancients accordingly were 
far less successful in dealing with light than in dealing 
with solar and stellar motions. Still they did make a 
little progress. They satisfied themselves that light 
moved in straight lines ; they knew also that these lines 
or rays of light were reflected from polished surfaces 
and that the angle of incidence w T as equal to the angle 
of reflection. These two results of ancient scientific 
curiosity would constitute the starting point of the 
present course of lectures. 
Professor Tyndall continued—Both of these are ca¬ 
pable of the easiest experimental illustration, but in the 
first place it may be useful to say a few words regarding 
the source of light to be employed in our experiments. 
The rusting of iron is, to all intents and purposes, the 
slow burning of iron. It develops heat, and if the heat 
be preserved a high temperature may be thus attained. 
The destruction of the first Atlantic cable was probably 
due to heat developed in this way. Other metals are 
still more combustible than iron. You may light strips 
of zinc in a candle flame, and cause them to burn almost 
like strips of paper. But beside combustion in the air 
we may also have combustion in a liquid. Water, for 
example, contains stores of oxygen, which may unite 
with, and thus consume a metal immersed in it. It is 
from this kind of combustion that we are to derive the 
heat and light employed in the present course. 
Their generation merits a moment’s attention. Before 
you is an instrument—a small voltaic battery—in which 
zinc is immersed in a suitable liquid. Matters are so 
arranged that a strain is set up between the metal and 
the oxygen ; actual union, however, being avoided. 
Uniting the two ends of the battery by a thick wire, the 
attraction is satisfied, the oxygen unites with the metal, 
the zinc is consumed, and heat, as usual, is the result of 
the combustion. A power, which for want of a better 
name, we call an electric current, passes at the same 
time through the wire. 
Cutting the thick wure in two, I unite the severed ends 
by a thin one. It glows with a white heat. Whence 
comes that heat ? The question is well worthy of an 
answer. Suppose in the first instance, when the thick 
ware was employed, that we had permitted the action to 
continue until 100 grains of zinc were consumed, the 
amount of heat generated in the battery would be capa¬ 
ble of accurate numerical expression. Let the action now 
continue with this thin wire glowing until 100 grains of 
