Copy 1

Practical pharmacy: the arrangements, apparatus, and manipulations, of the pharmaceutical shop and laboratory / By Francis [sic] Mohr ... and Theophilus Redwood.

  • Mohr, Francis.
Date:
1849
Catalogue details

Licence: Public Domain Mark

Credit: Practical pharmacy: the arrangements, apparatus, and manipulations, of the pharmaceutical shop and laboratory / By Francis [sic] Mohr ... and Theophilus Redwood. Source: Wellcome Collection.

    86/424 (page 74)
    rises, the sum of its sensible and latent heat is always the same. Thus, Water evaporating at 32° has 1180° of latent heat = 1212° . 7 LOD? Spa tla? FE — 1219° : ‘ 212° ,, 1000° f — 1212° ” 9 300° ” Onee ” ee Loo? It will therefore be evident, that, in evaporating a liquid, exactly the same amount of heat is always required, whatever process may be adopted ; whether it be by boiling under the pressure of the atmosphere, by spontaneous evaporation, or evaporation in vacuo, in each case the heat required for the vaporization of a given quan- tity of liquid will be the same, and this quantity for water will be equal to 1212°, as the amount of sensible and latent heat. Fig. 71 represents a smaller apparatus, which I have been accustomed to use for experimental purposes: it will serve to illustrate the essen- tial parts of a vacuum-pan, in its most simple form. <A, is a jacketed-pan supported on a cast-iron stand. There is a thick brass flange to the top of this pan at x a, which is ground to a smooth surface in the same way as the plate of an air-pump is. The top or head (B) also has a similar flange, which is ground so as to fit closely on to that of the pan. Between these two flanges is placed a washer of vulcanized India-rubber, which is compressed by four screws, two of which are seen at z 2, and a perfect air- tight union is thus made, which may be disconnected and re-formed with very little trouble. Before trying the vulcanized India-rubber, I found it very difficult to make a sound temporary joint between the pan and its cover, without using some substance the presence of which was objectionable. Common India-rubber cannot be used, on account of the action of the heat upon it, but when vuleanized, it is no longer affected by the heat to which it has to be subjected, and in every respect it fulfils all that is desired. The vulcanized India-rubber is sold in sheets about the sixteenth of an inch in thickness, out of which the washer must be cut in one plece, allowing a little for its expansion when compressed. Two circular plates of thick glass are inserted on two opposite sides of the cover of the pan, as shewn at O, so as to enable the operator to observe the progress of the inspissation in the pan. The neck is fixed to the head of the pan in such a manner, that, by means of a groove inside the head, just above the flange, whatever vapour is condensed in the head is carried off by the neck instead of returning to the contents of the pan. The beak of the neck is attached by an air- tight joint to a condenser (1); and the lower end of the worm of this condenser is inserted into a two-necked bottle (K), from the