IMPERFECT DEFECATION BY HEAT ALONE 165 
The advantage of the auxiliary action of heat in defeca- 
tion has never been questioned ; it is, in fact, wholly indis- 
pensable; but it is a great mistake to ascribe to its agency 
more than is due, and to make that the sole agent which 
cannot in any case rank higher than a subordinate. Much 
less warrant is there for the assertion that the purifying 
virtue of ‘“‘a simple active heat’ is of a superior quality 
when the evaporating surface is made to take the form of 
a crooked channel by means of a series of metallic strips 
placed transversely, extending nearly across the pan from 
the opposite sides. 
No peculiar advantage in defecation by this mode is 
discernible, but the reverse; for each time that the cur- 
rent of juice passes to the side of the pan it is compelled 
to pass through the dense body of scum settled there, and 
much of the feculent and mucilaginous matter which had 
already been separated from the juice at the heated center 
of any one of the transverse channels, soon becomes firmly 
incorporated with the same juice again, when the latter, 
rendered more dense by evaporation, passes onward through 
it, and this deleterious effect is produced as often as the 
current is led from side to side. Nor does the novelty of 
this mode of evaporation more deserve to pass unques- 
tioned than its merits. It may be original, but it is cer- 
tainly not new. Prof. McCulloh, in his work (Reports of 
Scientific Investigations in Relation to Sugar and Hy- 
drometers, revised edition, p. 237), describing various 
arrangements of evaporating surfaces, and particularly 
inclined planes, with a grooved or undulated surface to 
diffuse and retard the descent of the syrup, says: 
‘“M. Derosne has invented an apparatus of this kind, in 
which he causes the liquid to traverse the whole surface of 
the inclined plane, by means of numerous strips of metal 
placed across, and which are not quite as long as the in- 
