There are many forms of apparatus of this kind, one of which is shown in Fig. 22, but a more extended description of them is not necessary. The disadvantages of this process as compared with Knorr’s, are quite apparent. The connections with the evaporating flask and condenser are made with cork stoppers, which must be previously thoroughly extracted with ether and alcohol. These corks soon become dry and hard and difficult to use. The joints are likely to leak, and grave dangers of explosion arise from the vapors of the solvents escaping into the working room. Moreover, it is an advantage to have the sample warmed by the vapors of the solvent during the progress of the extraction, provided the liquid in direct contact with the sample does not boil with sufficient vigor to cause loss. The use of extraction apparatus with ground glass joints is also unsatisfactory. By reason of unequal expansion and contraction these joints often are not tight. They are also liable to break and thus bring danger and loss of time. =41. Compact Extraction Apparatus.=—In order to bring the extraction apparatus into a more compact form, the following described device has been successfully used in this laboratory.[19] The condenser employed is made of metal and is found entirely within the tube holding the solvent. This form of condenser is shown in Fig. 23, in which the tube E serves to introduce the cold water to the bottom of the condensing device. The tube D serves to carry away the waste water. The tube F serves for the introduction of the solvent by means of a small funnel. When the solvent is introduced and has boiled for a short time, the tube F should be closed. In each of the double conical sections of the condenser a circular disk B is found, which causes the water flowing from A upward to pass against the metallic surfaces of the condenser. A section of the double conical condenser is shown in the upper right hand corner. It is provided with two small hooks _hh_, soldered on the lower surface, by means of which the crucible G can be hung with a platinum wire. The condenser is best made smooth and circular in form. The crucible G, which holds the material to be extracted, can be made of platinum, but for sake of economy also of porcelain. The bottom of the porcelain crucible is left open excepting a small shelf, as indicated, which supports a perforated disk of platinum on which an asbestos film is placed. [Illustration: FIGURE 23. COMPACT CONDENSING APPARATUS.] The whole apparatus is of such size as to be easily contained in the large test-tube T. The mouth of the test-tube is ground so as to fit as smoothly as possible to the ground-brass plate of the metallic condenser P.