EEE 
ciently heated to insure disinfection. 
Oct. 14, 1886] 
NATURE 
583. 
(4) The higher specific heat of steam than of air, 
(5) The greater diffusive power of steam than of air. 
(6) The effects of pressure. By applying steam under pressure, 
relaxed and reapplied from time to time, so as to displace the 
cold air remaining in the interstices of the material, we havea 
means of considerably increasing the penetrative power of the 
steam, 
In view of the superior efficacy of steam, both in the destruc- 
tion of infective matters and in the penetration of badly-conduct- 
ing materials, some experiments were made with moist air in 
the hope that it might be found possible to obtain the advantages 
of the use of steam without its drawbacks. 
In these experiments either an evaporating vessel containing 
water was placed at the bottom of the hot-air chamber, or steam 
evolved in a separate boiler was led into the chamber by a pipe. 
An attempt was made to measure the degree of humidity of 
the air by suspending in the chamber two maximum-registering 
thermometers arranged side by side, one of them having its bulb 
covered with gauze kept moist by dipping in a phial of water, 
as in the wet-and-dry-bulb arrangement employed by meteoro- 
logists. It appears, how-ver, that there are no tables or 
formulz in existence by which the degree of humidity of the air 
corresponding to a given difference between the wet and dry 
bulb thermometers at these high temperatures can be ascer- 
tained. ‘The conditious in a heated chamber are so different 
from those met with in meteorological practice, that it is doubt- 
ful whether the relative humid. ty of the air could be obtained in 
this way with any great degree of accuracy ; but a comparison 
of the readings of the wet and dry bulb thermometers was found 
in practice to be useful as a rough indication of the dryness or 
dampness of the air, although the readings could not be reduced 
to a common measure. 
The experiments seem to show conclusively that moistening 
the air of the heated chamber diminishes the time necessary for 
the penetration of heat into a badly-conducting object. As 
examples the following observations may be quoted. They 
were made in an iron chamber heated by a furnace underneath, 
and furnished with a pipe by which steam could be admitted. 
Asmall jet Large jet 
Bes of eae of son 
admitted admitted 
Maximum readings of ( Dry bulb 299° F. ... 299° F. ... 249° F. 
thermometers hung 
up in chamber... | Wet bulb 146° Ob 190° 
Temperature attained in centre 
of similar pillows exposed for > 136° . 188° 209° 
one hour in heated chamber 
The moistening of the air of the heated chamber by either 
method was further found to have the advantage of rendering 
more equable the distribution of temperature in different parts 
of the chamber, thus tending to prevent scorching of the articles 
placed therein. 
On the other hand it was not found that the presence of 
moisture in proportions such as these, or even greater, increased 
the disinfecting effect at the temperature employed ; spores of 
the bacillus anthracis vetained their vitality equally well in 
heated air whether it were moist or dry ; thus they caused the 
death of a guinea-pig after exposure for an hour to a tempera- 
dry bulb 220° F. 
wet bulb 190° F. 
current of steam at 212° F. was sufficient to render them inert. 
To avoid risk of injury to articles subjected to disinfection by 
heat is an important practical question, not only on account of 
the value of the articles themselves, but also because, if the 
exposing of such articles to heat be attended with risk of injury, 
there is danger lest, to avoid this risk, they may not be suffi- 
The following are the 
principal modes in which injury may occur ; they are somewhat 
different in the case of steam from that of dry heat :— 
1. Scorching or partial decomposition of organic substances 
by heat. In its incipient stages this manifests itself by changes 
of colour, changes of texture, and weakening of strength. 
2. Overdrying, rendering materials brittle (by dry heat). 
3. Fixing of stains, so that they will not wash out. 
4. Melting of fusible substances, as wax and varnish, and 
ignition of matches accidentally left in pockets. 
5. Alterations in colour, gloss, &c., of dyed and finished 
goods, 
6. Shrinkage and felting together of woollen materials. 
ture of whereas five minutes’ exposure to a 
7. Wetting (by steam). 
Scorching begins to occur at different temperatures with 
different materials, white wool being soonest affected. It is 
especially apt to occur where the heat is in the radiant form. 
To avoid risk of scorching the heat should not be allowed much 
to exceed 250° F., and even this temperature is too high for 
white woollen articles. 
By a heat of 212° and upwards, whether dry or moist, many 
kinds of stains are fixed in fabrics so that they will not wash out. 
This is a serious obstacle in the way of the employment of heat 
for the disinfection previous to washing of linen, &c., soiled by 
the discharges of the sick. 
Steam disinfection is inapplicable in the case of leather, or of 
articles that will not bear wetting. It causes a certain 
amount of shrinkage in textile materials, about as much 
as an ordinary washing. ‘The wetting effect of the steam may 
be diminished by surrounding the chamber with a jacket con- 
taining steam at a higher pressure, so as to superheat the steam 
in the chamber. 
For articles that will stand it, washing in boiling water (with 
due pr2cautions against re-infection) may be relied on as an 
efficient means of disinfection It is necessary, however, that 
before boiling the grosser dirt should be removed by a pre- 
liminary soaking in cold water. This should be done before 
the linen leaves the infected place. 
The objects for which disinfection by dry heat or steam is 
especially applicable are such as will not bear boiling in water, 
e.g., bedding, blankets, carpets, and cloth clothes generally. 
Apparatus for disinfection by heat may be classified as 
follows :— 
(a) By hot atr— 
I. Apparatus in which the heat is applied to the outside o 
the chamber, and the products of combustion do not 
enter the interior. 
2. Apparatus in which the heated products of combustion 
enter the interior. 
3. Apparatus heated by steam or hot water circulating in 
closed pipes. 
4. Apparatus in which air previously heated is blown into 
the chamber. 
(b) By steam— 
5. By a current of free steam. 
6. By steam confined in a chamber at pressures above that 
of the atmosphere. 
The most important requisites of a good apparatus for disin- 
fection by heat are (a) that the temperature in the interior shall 
be uniformly distributed ; (6) that it shall be capable of being 
maintained constant for the time during which the operation 
extends ; and (c) that there shall be some trustworthy indication 
of the actual temperature of the interior at any given moment. 
Unless these conditions be fulfilled, there is risk, on the one 
hand, that articles exposed to heat may be scorched, or on the 
other hand, that through anxiety to avoid such an accident the 
opposite error may be incurred, and that the articles may not be 
sufficiently heated to insure their disinfection. 
In dry-heat chambers the requirement (a) is often very far 
from being fulfilled, the temperature in different parts of the 
chamber varying sometimes by as much as 100°. This is 
especially the case in apparatus heated by the direct application 
of heat to the floor or sides of the chamber. The distribution of 
temperature is more uniform in proportion as the source of heat 
is removed from the chamber, so that the latter is heated by cur- 
rents of hot air rather than by radiation. 
There is a marked difference between the distribution of 
temperature in a chamber heated primarily by radiant heat and 
in one heated by the admission of hot air or steam. Radiant 
heat is most intense close to its source, diminishing rapidly as we 
recede therefrom. Also it does not turn corners, and thus 
objects lying behind others are screened from it, except so far as 
it may be reflected upon them from other surfaces. The rays 
strike the walls of the chamber and objects therein, so that these 
are more highly heated than the air, which becomes heated only 
secondarily by contact with them. 
On the other hand, if air already heated, or steam, be ad- 
mitted into a chamber, the temperature tends to equalise itself in 
the different parts, and the walls and solid contents of the 
chamber do not become hotter than the air. 
In chambers heated by gas, when once the required tempera- 
ture has been attained, but little attention is necessary to maintain 
it uniform, and in the best-made apparatus this is automatically 
