FEBKUARY 21, 1907 | 
INA TORE 391 
is very great along the floor, immediately above the 
surface of the molten metal, falling off very rapidly as 
the roof of the tube is approached. It has always 
appeared to me probable that we are dealing with clusters 
of molecules, though there may be some simpler 
explaining the very steep density gradient. At all events, 
local heating of the denser portion of the vapour reduces 
its density, it seems to me, to a much greater degree 
than would be the case with an ordinary gas. The steep 
density gradient only occurs when the top of the hori- 
zontal tube is cooler than the floor, that is, cool enough 
to condense the vapour. The tubes I usually exhaust to 
a pressure of a millimetre or two, and I have always found 
it difficult to explain how it is possible to have a layer 
of vapour along the floor so dense that it is deep violet 
in colour, while along the roof the vapour shows no trace 
of colour at all. On the kinetic theory, it seems to me 
that we should expect the vapour to be moving rapidly 
from the floor to the roof, without, however, showing 
much difference in density at different points. Tt may be, 
however, that the traces of hydrogen which are present 
may be the cause of the phenomenon. What we call 
““very dense sodium vapour’ along the floor of the tube 
may be pure sodium vapour at a pressure of only a 
couple of millimetres. Along the roof we may have nearly 
pure hydrogen at the same pressure, and at intermediate 
points mixtures of the two in varying proportion, the 
sodium working its way up through the hydrogen and 
condensing on the roof. It will be well to try a very 
highly exhausted tube. 
Upon the whole, I think perhaps this is the most 
conservative’ way of looking at the thing, though my 
impression is that the hot wire produces a greater reduc- 
tion of density than we should expect on this assumption. 
Baltimore, February 5. R. W. Woop. 
A New Chemical Test for Strength in Wheat Flour. 
Tuat different wheats make flours of very different 
baking values has been known for a long time, and is 
emphasised by the fact that English millers are at the 
present time paying several shillings per quarter more for 
certain foreign wheats than for home-grown wheat. 
Baking value, or strength as the millers and bakers call 
it, is a subject of much interest, and many workers have 
tried to connect it with some definite physical or chemical 
property of the grain or flour. Thus it has been stated 
to depend on the percentage of gluten, the percentage of 
gliadin, or the ratio of gliadin to gluten. 
None of these explanations has been found to meet all 
cases, nor is there any likelihood of finding any single 
factor which is capable of measuring so composite an idea 
as strength as understood by the miller or baker. 
The value of a flour to the baker depends on at least 
four distinct properties:—(1) the volume of the loaf a 
given quantity will produce, which may vary more than 
30 per cent.; (2) the amount of water which a given 
quantity will absorb in making a dough of proper con- 
sistency for baking, which may vary from one-half to 
three-quarters of its own weight; (3) the shape of the loaf ; 
and (4) such points as texture and colour of the bread. 
The baker, and apparently most of those who have 
attacked the problem, have confused these widely divergent 
properties under the single name of strength, and attempted 
to find one chemical or physical factor which will measure 
them all at once. 
In taking up this subject, it seemed to me that the 
most hopeful line was to treat each property as a separate 
problem, and as the question of size of loaf seemed 
simplest, I have for the most part confined my attention 
to that aspect of the investigation. 
In converting a given amount of flour into a loaf of 
bread, the flour is mixed with water and yeast, and 
allowed to ferment for some time. It is then put into 
the oven and baked. The yeast finds sugar in the flour, 
feeds on this, and converts it into alcohol and carbon 
dioxide, and the volume of the loaf must depend cither 
on the volume of carbon dioxide evolved, or on the power 
of the flour to hold this gas. 
To test this a number of flours were obtained from Mr. 
A. E. Humphries, chairman of the Millers’ Association, 
NO. 1947, VOL. 75] 
way of | 
tested them in the bakehouse, and deter- 
The scale of strength adopted is a 
The mark 100 is assigned to the 
and o to a flour which is quite 
who had kindly 
mined their strength. 
purely arbitrary one. 
best flour on the market, 
unbakeable. 
In each experiment 20 grams of flour were mixed with 
20 c.c. of water and half a gram of standard yeast, in- 
cubated at 35° C., and the carbon dioxide liberated directly 
measured. The results are appended :— 
Baking value or COvevolved 
Reference No. “streneth ” cc. 
I 96 Ac : 270 
ze 90 wae 325 
3 73 . “ 274 
4 68 arc 55: 227 
5 65 sie es 205 
6 45 a Sos 156 
7 3 sé tos 131 
8 20 ; 287 
It will be seen that ‘with the exception of Nos. 1 and 8 
the order of strength and of carbon dioxide evolved are 
the same. Perhaps the greatest confirmation of the idea 
that strength is directly dependent upon the capacity of a 
flour for acting as yeast food is found in the apparent 
exceptions. On inquiry from Mr. Humphries, I learned 
that the high mark assigned to flour No. 1 was based 
upon bakings made after the addition of malt extract, 
while the low value given to No. 8 was based on baking 
tests made some months earlier. The high carbon dioxide 
value actually found for the latter enabled me to predict 
that the flour must have changed in composition so as to 
have gained in strength, and this prediction was verified. 
On baking again it was marked 40, with the report that 
it made a large loaf, and would have been marked higher 
but for the bad shape. , 
The quantity of carbon dioxide given off by a dough 
will depend upon two things—the sugar present as such in 
the flour, and the diastatic capacity. Analysis showed 
that in the flours experimented with the sugar present 
varied from 2-56 per cent. in the strongest to 1-60 per 
cent. in the weakest, and followed very closely the order 
of strength throughout the series. Diastatic capacity has 
not yet been thoroughly examined. 
The addition of sugar to flour was found always to 
increase the volume, the weight, and the height of the 
loaf. In a typical experiment made with household flour 
the increases were as follows :—volume, 13 per cent. ; 
weight, 2 per cent.; and height, 30 per cent. 
These experiments seem to prove conclusively that the 
volume of the loaf depends in the first instance upon the 
amount of sugar available in the dough, and a ready test 
is thus provided for that aspect of strength which is con- 
cerned with the size of the loaf. The other factors in- 
cluded in strength are at present under investigation. 
: T. B. Woop. 
Department of Agriculture, Cambridge. 
The Flight of an Elongated Shot. 
WirHin the limits of accuracy of this discussion, it may 
be assumed that the sections of the shot normal to its 
axis of figure are circular, that its C.G. is in the axis of 
figure, and that this axis and all the diameters of the 
circular section at the C.G. give the directions of the prin- 
cipal axes of inertia at the C.G. Angular momenta will 
be referred to the C.G., the axis of the shot will be called 
simply the axis, and all directions will be understood as 
viewed from behind the shot. 
The chief disturbing forces are the normal pressures of 
the air, the frictional forces being of a secondary order of 
magnitude. These normal pressures will be at a maximum 
upon the ogival head of the shot. The areas of such 
relatively smaller pressures as are due to vortex motion 
in the air, and to the partial vacua set up behind advancing 
surfaces directly presented to and against the air, will be 
situated towards the base of the shot, and upon the upper 
or the lower side of the shot, according as the axis is 
pointed above or below the tangent to the path of the 
C.G., i.e. the tangent to the trajectory. 
Now, from the first moment of the free motion the 
tangent to the trajectory falls away more and more from 
the axis of the shot. The immediate result of this is the 
