140 
NATURE 
[APRIL TI, 1912 
y 
The portions of the book devoted to the effects 
of soot on vegetation and the influence of deposits 
from smoke on the assimilation of carbon dioxide 
by the growing plant are specially well done, as 
is also the influence of smoke on the intensity of 
light, and the effects of sulphuric acid cn vegeta- 
tion. In these portions of the book the effect 
of smoke deposits in dwarfing and finally killing 
Clarendon Road 
15°2 
Weetwood Lane | 
Headine'ey | 
100 
52°8 
Fic. 
town vegetation is shown clearly to be due to at 
least three well-defined actions—(r) the blocking 
up of the stomata by soot; (2) the reduction of 
the intensity of sunlight by the coating formed 
on the leaf, which reduces the assimilation of 
carbon dioxide; and (3) by the action of sulphuric 
acid partly condensed in the soot and 
partly in the rain water. 
The photograph (Fig. 1) repro- 
duced here from the book shows in 
a striking way the effect of locality 
on the development and power of 
assimilation possessed by the leaf. 
The laurel leaf grown at Weet- 
wood Lane on the outskirts of 
Leeds shows in marked contrast to 
the one from the City Square, which 
may be taken as the centre of the 
town, the assimilative power of the 
latter being only 11°6 per cent. of 
the former. 
The disappointing part of the book 
is that which deals with the nature 
of smoke and the soot which it con- 
tains, and from the commencement 
of the first division on page 4 it is 
marked by loose expressions. For 
instance, we read that “soot is a pro- 
duct of incomplete combustion, and 
is formed partly by the mechanical 
removal of dust by the chimney 
draught, and partly by the decomposition of the 
fuel, such as occurs in the process of destructive 
distillation.” Dust is not, a rule, a product 
of incomplete combustion, nor is the tar and free 
carbon formed in the destructive distillation of 
coal. 
Again, on page 5, analyses of soot from various 
sources are given, and also analyses of the coal 
NO. 2215, VOL. 89] 
as 
that gave rise to them, from which the reader 
learns that these “original ” coals contained o'88, 
o'92, and 1°64 per cent. of tar respectively. 
Surely the authors do not believe that a ton of 
these coals contains about a couple of gallons 
of ready-made tar. 
y.—Laurel leaves and their respective assimilations. 
Fic. 
In describing the experiments by which they 
sought to ascertain the amount of soot carried’ 
up the chimney, they say, “The 
chimney gases were drawn off at 
the rate of about a litre a minute, 
which would approach the speed 
of the gases passing up the flue,” 
and they add that a good fire was 
maintained all the time. They 
probably mean that the rate of 
flow through the asnine tube 
was about that of the rate of flow 
in the flue, but they do not say 
so, and if ine flue draught was a 
litre a minute, it is no wonder 
their figures are abnormal. 
The method of taking the 
| Seppe dun carbon in the carbon dioxide 
of the flue gas as representing 
the amount of carbon burnt 
on the fire cannot give anything but in- 
correct results: if soot is formed, there is. 
incomplete combustion, and carbon monoxide 
and hydrocarbon gases are also produced, and 
the percentage of soot found will be far too high. 
In any case, the percentage of soot to carbon 
Black fringe of soot on Coniston Lake, Lake District. 
burnt is of no practical importance. It is the 
percentage of loss on fuel used that is the im- 
portant factor, and the soot is only a small pro- 
portion of this, unburnt hydrogen and hydro- 
carbon vapours and gases being by far the most 
important items. 
The authors 
generalisations, 
in broad 
discussing 
evidently believe 
and on page 61, in 
