390 
NATORE 
| FEBRUARY 21, 1907 
OUR 'BOOK SHELF. 
Penrose’s Pictorial Annual. The Process Year Book 
for 1906-7. Edited by William Gamble. (London : 
A. W. Penrose and Co., Ltd., n.d.) 
Tuts valuable and beautifully got-up volume sur- 
passes, if possible, its predecessors. In the last few 
years the colour process has been rapidly coming to 
the front, and the present issue of this annual gives 
the reader an excellent insight into the good quality 
of the results which may be secured by the best pro 
cesses of the day. The editor’s task has evidently 
been no light one to include in this volume the wealth 
of material that is available, but the reader will be 
more than satisfied when he peruses it himself. 
The arrangement of the book is the same as in 
former years. A most interesting series of articles 
dealing with process work and allied subjects is con- 
tributed, and the names of the authors are a sufficient 
guarantee for them. Thus, to mention only one or 
two cases, the editor gives a brief but clear account 
of the recent progress in process work, while Major- 
General Waterhouse describes the work of M. Léon 
Vidal, who, as he says, was a man who “ fully recog- 
nised the educational value of photography,” and who 
did much for its development, especially in the direc- 
tion of photomechanical work, and the practical ap- 
plication of permanent printing processes for book 
illustration. M. Vidal’s last contribution to this 
annual is contained in the present volume, and is 
entitled ‘‘ The Future of Colour Photography when 
Autochrome Plates come into General Use.”’ 
Turning from the text to the illustrations, we have 
here also much food for thought. The frontispiece 
is an admirable engraving of Charles I. by the Rem- 
brandt Intaglio Printing ox Ltd. Of the numerous 
three- or four-coloured “illustrations, mention may be 
made of those opposite p. 8, entitled “ Still Life,” by 
Messrs. John Swain and Son Ltd.; opposite p. 128, 
entitled “Dessert,” by Messrs. H. Kollien and Co. ; 
and following p. 136, entitled “Mimosa Blossom,” 
by Messrs. Hood and Coz, td: 
Einfiihrung in die mikroskopische Analyse dey Dro- 
genpulver. By Dr. L.« Koch. Pp. witi+174. 
(Berlin: Gebriider Borntraeger, 1go06.) Price 4 
marks. 
THE microscopical examination of drugs for the pur- 
pose of gaining an accurate knowledge of their con- 
stitution and of learning to detect impurities and 
adulterations is now recognised as a necessary part 
of the usual courses for pharmaceutical students, and 
as many chemists endeavour to acquire part of their 
knowledge during the term of their apprenticeship, 
they require books of this nature to help them in 
their independent studies. 
Dr. Koch has prepared this elementary manual as 
an introduction to the specialised vegetable histology 
that affords the principal means of distinguishing 
pharmaceutical products with the aid of the micro- 
scope. A few examples of well-known drug's selected 
as specimens of bark, seed, and other plant products 
are described in detail, and the elements are figured. 
The instructions are so minute and therough that a 
student using the book intelligently should soon 
become proficient in histological determination. The 
chapter on methods is not, however, so complete as 
would be expected. Although powdered prepara- 
tions are generally used for investigations, it is at 
least desirable that the student in his training should 
become efficient in section-cutting. Further, a more 
extensive account of reagents would be helpful, for 
while agreeing with the substitution of chloral hydrate 
in place of potash, there seems no reason for leaving 
out potash altogether, or sulphuric acid and several 
other recognised testing solutions. 
NO. 1947, VOL. 75] 
LETTERS TO THE EDITOR. 
[The Editor does not hold himself responsible for opinions 
expressed by his correspondents. Neither can he undertake 
to return, or to correspond with the writers of, rejected 
manuscripts intended for this or any other part of NATURE. 
No notice is taken of anonymous communications.] 
An Occurrence of Helium in the Absence of 
Radio-activity. 
I MENTIONED in Nature a few weeks ago (January 17 
p. 271) that I was engaged in examining the inert gases 
contained in ordinary (inactive) minerals. A result has 
been obtained so surprising that it seems worthy of 
immediate record. I have found that beryl contains a 
quantity of helium of quite a different order of magnitude 
from what is found in ordinary inactive minerals. Thus 
250 grams of beryl from New Hampshire gave 4-2 c.c. of 
helium on heating. The mineral appears to be absolutely 
without radio-activity. A tray of the powder, placed in 
the case of an electroscope of exceptionally small natural 
leak, did not increase that leak to any measurable extent. 
It seems likely that we have here a case of rayless 
change. In all probability beryllium is the constituent of 
beryl which is concerned. It is hoped to test this view 
further by the comparison of different minerals. 
R. J. Sirupr: 
Sunnyside, Cambridge, February 19. 
The Rusting of Iron. 
SEVERAL letters have appeared in NATURE respecting the 
conditions under which iron rusts. The usually accepted 
view has been that iron will not rust unless carbonic acid 
is present. After a very careful investigation of the sub- 
ject, I was led to the conclusion that provided iron, 
oxygen, and liquid water are brought together, chemical 
change takes place with the production of rust, even when 
every precaution has been taken to exclude even traces of 
carbonic acid, and that therefore some other explanation 
must be found for the fact that alkalis inhibit the rust- 
ing of iron. An explanation has also to be found for the 
fact, established in the course of this investigation, that 
if polished iron is immersed in a solution of potassium 
dichromate, rusting is completely inhibited, and the surface 
of the metal remains perfectly bright (Dunstan, Jowett, 
and Goulding, Journ. Chem. Soc., 1905). 
Dr. Gerald T. Moody has recently given (Journ. Chem. 
Soc., 1906) an account of experiments he has made, from 
which he concludes that carbonic acid is essential to the 
rusting of iron, and that rusting does not occur in its 
absence. 
As these experiments were made under somewhat 
different conditions from mine, they have been repeated. 
The results obtained are, however, not confirmatory of 
the conclusion that carbonic acid is essential to the rusting 
of iron. 
This apparently simple chemical change requires addi- 
tional experimental study, and I hope shortly to be able 
to make some further contribution to the subject. 
February 19. Wynpnam R. Dunstan. 
Ionisation and Anomalous Dispersion. 
Tue experiment recently described in a letter in NaTuRE 
by Dr. Schott (January 17, p. 271) does not appear to me to 
have any very direct bearing upon ionisation. There appears 
to be no question but that the changes observed in the dis- 
persion curye were due to an alteration in the optical 
density gradient of the sodium vapour, resulting from local 
heating by the wire. The experiment is very similar to one 
which I made two years or more ago, during an examin- 
ation of the physical properties of the vapour. A wire was 
stretched through the tube, along its axis, and heated by 
a current. The vapour was observed to be much less 
dense around the heated wire. The observations were 
made by looking through the tube either at a sodium 
flame, or a lamp behind bluish-green glass (for which light 
the vapour was very opaque). On heating the wire a 
clear space appeared around it. If I remember rightly, I 
never published this result, as the experiment was one of 
a series which has not, even yet, been completed. 
In a sodium dispersion tube the density of the vapour 
