Marcu 14, 1912] 
NATURE 
29 
nfortunately, there is a tendency to adopt an 
exaggerated terminology, and to obscure the 
roblems by complicated methods of treatment 
instead of striving after the simplest possible 
language. In consequence, the subject is invested 
ith a mysticism which is quite unnecessary. 
For this reason a book of the type written by 
Dr. Arndt is to be welcomed, and the fact that 
an edition has been exhausted already shows that 
the work has met a demand. 
Following a brief introduction, which, although 
necessarily condensed, is written in relatively 
simple style, attention is directed in turn to a 
number of industries in which the materials 
handled are colloids. It is the aim of these sec- 
tions to emphasise the fact that the substances 
oncerned are colloids rather than to explain their 
ehaviour in practice. The list is a very exten- 
‘sive one, ranging from such inorganic materials 
as glass, tungsten lamp filaments, pottery, and 
cements to organic industries, including dyeing, 
tanning, soap-boiling, brewing. Finally, refer- 
ence is made to the part played by colloids in 
sewage disposal and in agriculture. The exam- 
ples are very comprehensive, and serve to show 
how generally colloids enter into industrial 
operations. 
The discovery by Siedentopf and Zsigmondy 
of the ultra-microscope, an instrument whereby 
the single particles in colloid solutions are made 
visible, has facilitated greatly the investigation of 
colloidal solutions of metals. In the manufacture 
of ruby glass, for example, gold chloride is added 
to the molten glass; when quickly cooled this 
is colourless, but on subsequent heating up to 
the point of softening, it suddenly becomes ruby 
red. The ultramicroscope shows the presence in 
the coloured glass of colloidal gold particles; in 
the colourless glass none are to be seen. The 
explanation is that at first the gold particles 
are too small to colour the glass; on heating, 
they increase in size and give rise to the 
colour. 
Baye. A. 
PRACTICAL PYROMETRY. 
Pyrometry: a Practical Treatise on the Measure- 
ment of High Temperatures. By Chas. R. 
Darling. Pp. xii+200. (London: E. and 
F. N. Spon, Ltd.; New York: Spon and Chaim- 
berlain, rgr1.) Price 5s. net. 
ITHIN recent years pyrometry has become 
an essential factor in a large number of 
industrial operations where high temperatures are 
involved; particularly is this the case in the 
metallurgy of steel, where success or failure often 
NO. 2211, VOL. 89] 
entirely depends on correct adjustment of the tem- 
perature within narrow limits. Mr. Darling’s 
excellent series of Cantor lectures were therefore 
very welcome, and no less welcome and of wider 
service will this small volume, the outcome of these 
lectures, prove. 
The “practical man” has a love for the 
“practical” test in the furnace or kiln, and for 
many operations, such as those in pottery and 
china production, an actual firing test is to be 
commended, but generally manufacturers are 
devoting more attention to actual temperature 
measurements. Great advances have been made 
in recent years in perfecting forms of pyrometers 
suitable for works practice, amongst which men- 
tion may be made of temperature recorders con- 
tinuous in action, and pyrometers of the radiation 
type, first introduced by Féry in 1902. The later 
form of these instruments, with fixed focus, 
enables excellent measurements of furnace, molten 
metal, and other high temperatures to be taken 
by the simple process of directing the pyrometer 
at the object and reading the deflection on a suit- 
able portable galvanometer. 
The author deals in a comprehensive manner 
with the various types of instruments, and gives 
valuable advice as to the suitability of those of 
different classes for special purposes, and em- 
phasises the fact that choice of an unsuitable 
| pattern has often led to considerable menetary 
loss and the condemnation of an instrument which, 
in its proper sphere, would have proved satis- 
factory. 
After mentioning that for practical purposes the 
gas scale is in agreement with the thermo- 
dynamical scale of temperature, and serves as a 
standard of comparison for other instruments cf 
practical form, the author points out that com- 
parison is only possible to the present limit of the 
gas scale (1550° C.), and that beyond this the 
results can only be arrived at by extrapolation, 
which in some cases has led to grave errors. 
With instruments of the radiation type, however, 
assumption that the laws applicable for the lower 
ranges will hold for the higher ones appears to 
be justified. 
Mr. Darling is a clear and concise writer on a 
scientific subject which has wide commercial 
application, and his treatment of the subject of 
practical high temperature measurement in this 
volume will commend itself to the practical man, 
who, whilst requiring sufficient of the scientific side 
to understand the principles involved, does not 
require abstruse science in his handbooks. This 
volume, like the author’s well known “Heat for 
Engineers,” admirably fulfils these requirements. 
j. Ss) Soe 
