238 MAGNUS ON THE FORCE REQUISITE 
ture at which the liquid would boil without the presence of a 
foreign body. We should, however, be led to imagine that a 
smooth metallic surface, because it attracts the water more 
powerfully than the parts of the water attract one another, would 
not lower but raise the boiling-point, while experience teaches 
the contrary. But if a metallic surface, even when it has been 
most completely cleansed, be immersed in water, it adheres in 
general; but there are always some places where it does not 
adhere, and from which it withdraws itself, where therefore the 
attraction to the water is smaller than that existing between the 
parts of the water. The same is the case with glass, only when 
this has been purified by boiling in sulphuric or nitric acid does 
the water form a continuous coating, otherwise there are always 
found some spots where it does not adhere. Consequently the 
boiling-point, even in glass vessels which have been purified in 
the above manner, is, as was shown by M. Marcet, frequently 
5° C. higher than the temperature of the liberated vapour; and 
probably this is likewise the temperature at which the water 
would boil without the presence of a foreign body. On repeat- 
ing this experiment I did not find the boiling-point 5° C., which, 
as stated by Marcet, is not always readily attained, but yet 
several degrees higher than the temperature of the evolved steam. 
I have, moreover, attempted to clean a platinum dish by fusing 
caustic potash and then by sulphuric acid, and in this manner 
I have equally succeeded in raising the boiling-point of the water, 
but not so considerably.as with glass. This, probably, is owing 
to my platinum vessel having been already frequently employed 
and not being free from scratches, &c., which in this instance 
acted like pulverulent bodies; for these, as is well known, lower 
the boiling-point most, so that by the introduction of powdered 
glass or metal into boiling water, its temperature can scarcely 
be distinguished from that of the escaping steam. 
If, moreover, we bear in mind that towards each particle of 
dust which may fall in, the adhesion of the water is smaller than 
the cohesion of its parts, and that the adhesion of solid bodies — 
is modified by the most varied circumstances, so that as recent — 
discoveries show, light, heat, electricity, nay, even the mere vi- © 
cinity of another substance, modify the surface of a body to such — 
an extent that the vapours of water and mercury deposit them- 
selves at various places differently, it cannot be surprising if the © 
presence of metal or glass did not, except in some rare instances, 
