Controlled Evaporation with an Extended Hotplate Top The device shown in the figure enables the evaporation of sample solutions to smsll volume with a greatly reduced risk of baking them dry. This is of particular help in operations like reducing the volume of an aqueoos phase after isopropyl ether extractions, when some of the explosive peroxides which tend to form in the ether may transfer to the aqueous part. The device has been constructed to accomrnoditte 100-ml or 200-mI Beraelius beakers, and to fit on a standard Thermolyne 700 W hotplate with a. top 16 cm square. The msin aluminum hlock 25 rnm thick in milled to fit on the hotplate as shown, so the front face with controls is not ohstrueted, and is bored to receive six 20C-mI beakers. Sleeves with knurled Ranges are provided for 100-nd heskem The lower thin aluminum plate is supported by four screws with knurled (haG tery berminal) nuts st an adjustable distance below the main hlock. The beakers are supported on round-head machine screws tapped into this lower plate to allow free circulation of unheated air around the lower past of the hesker. At steady state, with the hotplate a t maximum setting, the surface temperilture on the surface of the extension ranged from 240°C aver the center of the in each of six 200-ml beakers, hotplsbe to 18O0C at, an outer corner. Under these conditions, 130 ml of water wit,h the support plate 15 mm helow the msin hlock, was evaporated to 30 ml in 3 hr. The evaporation of the remaining 30 ml required an additional 2 hr.
108 / Journal of Chemical Edvcotion
