Absorption train

The decomposition of the carbonate may be effected with dilute hydrochloric acid, dilute perchloric acid, or phosphoric(V) acid. The last-named acid is perhaps the most convenient because of its comparative non-volatility and the fact that the reaction can be more easily controlled than with the other acids. If dilute hydrochloric acid is employed, a short, water-cooled condenser should be inserted between the decomposition flask and the absorption train (see below). 

A 500-ml. three-necked round-bottomed flask is fitted with an efficient reflux condenser, a glycerol-sealed mechanical stirrer,1 a dropping funnel, and a gas inlet tube extending nearly to the blades of the stirrer (Note 1). An absorption train,2 with the addition in / of a safety tube which extends nearly to the bottom, is connected to the upper end of the reflux condenser (Note 2). A 2-cm. layer of water in J allows it to serve as a bubble counter K is one-third filled with a 50% potassium hydroxide solution. The entire apparatus is set up in subdued light in a hood and swept with dry hydrogen (Notes 3 and 4). Phenyl-magnesium bromide is prepared in the flask by the usual procedure 3 from 78.5 g. (0.5 mole) of bromobenzene, 12 g. (0.5 gram... 

The cellulose specimen under examination is refluxed in the acid-oxidant mixture and the gases formed are swept continuously into an absorption train by a carrier stream of air free of carbon dioxide. Conrad and Scroggie20 have added a number of important improvements which apparently increase the reproducibility of results. One of their modifications is a stirrer in the reaction chamber which reduces the danger of bumping caused by superheating. The latter is undesirable since the reaction is apparently quite sensitive to the temperature. 

The absorption train can then be detached, removed to the balance room, wiped carefully with a clean hairless cloth and kept 15—20 minutes to attain constant temperature. The tubes are then weighed without their rubber caps. If the apparatus is in proper working order, and the... 

The CaCla tube is attached with a piece of pressure tubing to the snout end of the combustion tube through the tube entering the glass bell. The first soda lime tube is attached to the CaC tube through the small tube entering under the stopper. The second soda lime tube is attached to the exit tube of the first in a similar manner. The absorption train is protected with a small tube containing CaClj and soda lime. 

The absorption train is composed of a tube packed with water absorbent, a second tube packed with a carbon dioxide absorbent, and a guard tube packed with equal volumes of the water and carbon dioxide absorbents. Anhydrous magnesium perchlorate (MgC104) is commonly used for the water absorbent, while sodium hydroxide (NaOH) or potassium hydroxide (KOH) impregnated in an inert carrier is used as the carbon dioxide absorber. 

Exhaust tube to absorption train -Synthesis of selenium dioxide. 

B) Preparation of a-Bromopropionic Acid (M.). Arrange a 500-ml Florence flask as shown in Figure 46, without the dropping funnel the absorption train is the same as used in the preparation of chloroacetic acid (page 225). The rubber stopper which connects the reflux condenser to the flask is painted with sodium silicate twice, and allowed to dry each time. 

Absorption trains of early ammonia oxidation processes to nitric acid were constructed of chemical stoneware or acid-proof brick, which restricted acid production to near ambient atmospheric pressure because of the low strength of the structural materials. The discovery that Duriron (silicon-iron) or high chrome stainless steels could tolerate these corrosive conditions well allowed the adoption of pressure absorption. This measure markedly decreased the size of the absorbers required and reduced nitrogen oxide stack losses. Pressure operation was easiest to achieve by compression of the feed gases at the front end of the process. In this way improved acid production is obtained at comparable capital costs per unit of product by operation at atmospheric pressure. 

In all cases a gaseous substance is formed. If this is to be collected, then it is passed through an absorption train to remove unwanted gaseous impurities. The desired gas then is either absorbed on a solid absorber and weighed or is passed into a solution where it reacts quantitatively with another chemical and the excess chemical is determined. Alternatively, the evolved gas mixture could be trapped and then passed through a gas chromatograph or the vapors can be examined spectrophotometrically. 

Place a small amouni of glycerine on the ends of each tube and connect the tubes back into the absorption train. 

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