. An introduction to practical pharmacy: designed as a text-book for the student, and as a guide to the physician and pharmaceutist. With many formulas and prescriptions . there is asimilar choice between placing it immediately over the source ofheat or in a less heated position near the edge of the bath. The Water Bath.—A good extemporaneous water bath is pre-pared by procuring a rather shallow tin or copper cup, and anevaporating dish of just such size as will completely cover it, pro-jecting slightly over its edge. Those glass evaporating dishes whichhave a projecting edge turned over and d
. An introduction to practical pharmacy: designed as a text-book for the student, and as a guide to the physician and pharmaceutist. With many formulas and prescriptions . there is asimilar choice between placing it immediately over the source ofheat or in a less heated position near the edge of the bath. The Water Bath.—A good extemporaneous water bath is pre-pared by procuring a rather shallow tin or copper cup, and anevaporating dish of just such size as will completely cover it, pro-jecting slightly over its edge. Those glass evaporating dishes whichhave a projecting edge turned over and downwards, will fit moresecurely over the metallic vessel, without beingpushed out of placeby the force used in stirring. They are also convenient from notallowing the ready escape of steam round the edges: this beingcondensed, either passes back into the cup, or drops from the edge. The outer vessel is to be nearly filled with water, and the sub-stance to be heated placed in the evaporating dish, which being THE WATER BATH. 147 adjusted to its place, the whole is put over the fire, as shown in In 142, the heat is applied directly by radiation. Fig. Now, the temperature of boiling water under ordinary circum-stances of pressure being 212°, it is obvious that the contents of theevaporating dish cannot reach a higher point; it is found practi-cally, that at least two or three degrees of heat are lost, in passing fromthe boiling water through the dish, so that when the water below isboiling, the temperature of the contents of the dish will not exceed210°. Aqueous liquids will not boil in a water bath, but most ofthe solutions used for the preparation of extracts being alcoholic,undergo active ebullition at this temperature. A disadvantage attending upon an extemporaneous arrangement,such as is shown above, arises from the rapid escape of steamfrom the lower vessel on all sides of the capsule: now the quantityof vapor which will be suspended in a given space in th
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Keywords: ., bookcentury1800, bookdecade1850, booksubjectpharmacy, bookyear185
