Apparatus, dispensing

The Dafert pipette (Fig. 3.2 Section 3.11) is a convenient apparatus for dispensing fixed volumes of a standard solution, as are also the various liquid dispensers which are available. 

Runs of other sizes may be made in the same apparatus. With half the quantity of sodium specified, temperature control demands much more attention. With larger quantities, the nickel crucible is dispensed with, and the carefully cleaned pot used. The checkers used 260-270 g. of sodium and averaged a yield of 94 per cent the reaction time was increased by only one-half hour. By arranging two series of apparatus in parallel, but connected to the same cylinder of ammonia, one operator can prepare twice as much amide in almost the same time. 

The special apparatus (Fig. 2) consists of two 500 ml Erlenmeyer flasks A and B having slightly rounded bottoms and fitted with Teflon -coated magnetic stirring bars and injection ports, a mercury-filled bubbler back-up prevention valve C, and a mercury-filled automatic dispenser D with airtight-connected insert delivery tube of a buret E. 

In some petroleum refineries or chemical plants, an on-site fire brigade that is equipped with an apparatus capable of dispensing large volumes of dry chemical, or a vehicle with a large-capacity carbon dioxide (C02) cylinder is common practice. 

Fig. 1.10. Transfer of air-sensitive liquids from metal cylinders, (a) A three-way metal stopcock constructed for use with syringes may be modified by the addition of a threaded fitting so that it mates with a lecture bottle. The side inlet is used to purge the apparatus initially and to blow liquid out of the syringe needle at the completion of the transfer. The cylinder is put under a low pressure of inert gas before the transfer is begun, (b) Sometimes air-sensitive liquids are sold in siphon-type cylinders, and the liquid from such a cylinder can be dispensed as shown here. As with the previous example, inert gas is used to force the liquid out of the cylinder.

Fig. 1.17, Apparatus for dispensing known quantities of condensable gases. The trap may be calibrated by using water (for large volumes) or mercury (for small volumes). A mercury bubbler is included to prevent blowing the apparatus apart.

Fig. 12.2 Thermistor array apparatus consisting of (a) eight reagent/ substrate reservoirs, (b) an 8-channel dispensing head, (c) a 96-well plate and holder (movable in the x-direction), (d) an 8xl2 thermistor array, (e) a base plate (movable in the z-direction), (f) a multiplexing apparatus, (g) a microcomputer.

This type of integrated chemical synthesizer comprises a device array of micronsized wells and connecting channels in a substrate that interfaces with a station for dispensing fluids to and collecting fluids from the array and for performing analytical measurements of material in the well. The station is also connected to control apparatus to control the fluid flow to the channels and wells and to collect measurement data from the substrate. All the mentioned elements are independent and together they can perform a variety of tasks in parallel [85],... 

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