Thistle funnel

Arsenic present only in traces (in any form) can be detected by reducing it to arsine and then applying tests for the latter. In Marsh s test, dilute sulphuric acid is added dropwise through a thistle funnel to some arsenic-free zinc in a flask hydrogen is evolved and led out of the flask by a horizontal delivery tube. The arsenic-containing compound is then added to the zinc-acid solution, and the delivery tube heated in the middle. If arsenic is present, it is reduced to arsine by the zinc-acid reaction, for example ... 

A funnel tube or thistle funnel, about 40 cms. long, which fits into the sealed tube and serves to convey the AgN03 and fuming HN03 to the bottom of this tube. 

The apparatus used takes several different forms, one of the simplest consisting of a two-necked Wolff s bottle, a thistle funnel being fitted into one neck and a gas delivery tube, connected with a calcium chloride tube, into the other. Beyond the calcium chloride tube is a hard glass tube, 40-45 cm. long and 5-6 mm. in diameter, drawn out at a certain position to a narrow, pointed tube. 

Hero s fountain is an old and, to some people, puzzling device. The bulb A is blown up to about 50 mm diameter and fitted with a jet tube extending almost to the bottom. An 8 mm tube is now joined to the bulb, near the ring seal, and bent over parallel to the jet tube. The jet tube is bent into the shape shown in Fig. 8.9, then constricted and drawn out into a short jet of not more than 1 mm bore. The thistle funnel B and bulb C are made with 8 mm connecting tubes as shown in Fig. 8.9. The 25 cm tube is bent into a U with parallel hmbs and as near to C as possible. 

A certain quantity of the substance to be tested is decomposed by one of the methods described on p. 329 et seq., for instance, by Ewins s method. The liquid obtained, which contains arsenious oxide, is reduced with zinc and hydrochloric acid, using an apparatus like that shown in Fig. 19. This consists of a bottle of about 30 ml. capacity, fitted with a two-holed stopper, carrying a small thistle funnel which passes to within i mm. of the bottom of the bottle, and a bent tube connected by a rubber stopper with another small tube. The latter has a glass bulb of about... 

A Woulfs bottle is taken and some pieces of granulated zinc are placed in it. Then a thistle funnel is fitted in one mouth and in the other mouth a delivery tube is fitted. Some water is added to cover the zinc pieces. Then cone. H2S04 or HQ is through the funnel. The hydrogen gas coming out of the Woulfs bottle through delivery tube is collected by downward displacement of water. 

The lower end of thistle funnel must be under water in the Woulfs bottle. 

A Woulf s bottle is taken and some pieces of marble, chalk or shells are put in it little of water is added to cover the marble. A thistle funnel and a dehvery tube bent at-right angles is fitted. 

Acid is added through the thistle funnel. The reaction occurs. The gas is collected by upward displacement of air. The gas is not collected over water because the gas is highly soluble in water. The gas can be tested with the help of a burning splinter. It extinguishes a burning splinter or a match stick. 

Pour about three ounces of strong sulphuric acid down the thistle funnel. The flask is then carefully heated—using a sand bath—the heat being lowered as soon as the action commences. The gas given oS is allowed to pass into the water, until the latter is saturated. This then becomes sulphurous acid. 

In the laboratory it is usually prepared as follows. some lumps or pieces of marble are placed iu a flask and hydrochloric acid poured down a thistle funnel (suflicient must be poured in to cover the bottom of the thistle funnel or the gas will escape up the thistle funnel). Since the gas is half as heavy again as... 

Hg. 11.11 An example of osmosis (a) the experiment water enters the thistle funnel from the less concentrated sugar solution (b) measuring osmotic pressure using an air supply. 

Figure 11.11(a) illustrates a simple laboratory osmosis experiment. At the end of the osmosis process the solution inside the thistle funnel has stopped rising. 

We cannot accurately use the height the sugar solution has risen during the osmosis as a measure of osmotic pressure. This is because the solution in the thistle funnel is less concentrated at the end of the experiment than at the beginning. Since a less concentrated solution is a less dense one, a simple measurement of h overestimates the osmotic pressure. 

A better way of measuring osmotic pressure is to apply a known amount of external pressure until the osmosis just stops. The applied pressure then exactly equals the osmotic pressure of the solution. The principle of this type of measurement is shown in Fig. 11.11(b). We start by connecting the top of the thistle funnel to a high pressure air supply. The pressure of the air supply is slowly increased so as to just stop the osmosis - this air pressure is equal to the osmotic pressure across the membrane. 

Ann.y 1868, cidvi, 265-83 Ges. Abhl.y iii, 434-48 with illustration of modern gas preparation apparatus with rubber stoppers and thistle-funnel. 

In the laboratory, carbon dioxide is usually prepared by the action of hydrochloric acid on marble, some lumps of the latter being placed in a flask and hydrochloric acid poured down a thistle funnel. Carbon dioxide being half as heavy again as air, the gas can be collected like chlorine in Experiment C7. It is a colourless gas, without smell and with a very faint acid taste, but slightly soluble in water. It should be allowed to bubble through water before it is collected in order to remove all traces of hydrochloric acid. 

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