A: Under a microscope,using a mixture of glycerin and water (1:1)as a mounting agent,it presents large and small granules,and very rarely,intermediate sizes.The large granules,usually 10µm to 60µm in diameter,are discoid or,more rarely,reniform when seen face-on.The central hilum and striations are invisible or barely visible,and the granules sometimes show cracks on the edges.Seen in profile,the granules are elliptical and fusiform and the hilum appears as a slit along the main axis.The small granules,rounded or polyhedral,are 2µm to 10µm in diameter.Between crossed nicol prisms,the granules show a distinct black cross intersecting at the hilum.

B: Suspend 1g of it in 50mLof water,boil for 1minute,and cool:a thin,cloudy mucilage is formed.

C: To 1mLof the mucilage obtained in Identification test B,add 0.05mLof Iodine solutionprepared as directed below:an orange-red to dark blue color is produced,which disappears on heating.

Procedure— Accurately weigh 6.0g of test substance containing about 2mg of nitrogen,transfer to a combustion flask,add 4g of a powdered mixture consisting of 100g of potassium sulfate,5g of cupric sulfate,and 2.5g of selenium,and add three glass beads.Wash any adhering particles from the neck into the flask with 5mLof sulfuric acid,allowing it to run down the sides of the flask,and mix the contents by rotation.Close the mouth of the flask loosely,for example by means of a glass bulb with a short stem,to avoid excessive loss of sulfuric acid.Heat gradually at first,then increase the temperature until there is vigorous boiling with condensation of sulfuric acid in the neck of the flask;precautions should be taken to prevent the upper part of the flask from becoming overheated.Continue the heating for 30minutes,unless otherwise prescribed.Cool,dissolve the solid material by cautiously adding to the mixture 25mLof water,cool again,and place in a steam distillation apparatus.Add 30mLof sodium hydroxide solution (42in 100),and distill immediately by passing steam through the mixture.Collect about 40mLof distillate in 20.0mLof 0.01Nhydrochloric acid and enough water to cover the tip of the condenser.Toward the end of the distillation,lower the receiver so that the tip of the condenser is above the surface of the acid.Take precautions to prevent any water on the outer surface of the condenser from reaching the contents of the receiver.Titrate the distillate with 0.01Nsodium hydroxide,using methyl purple TSas the indicator (n1mLof 0.01Nsodium hydroxide).

Reagents—

Apparatus— In this test,the sulfur dioxide is released from the test specimen in a boiling acid medium and is removed by a stream of carbon dioxide.The separated gas is collected in a dilute hydrogen peroxide solution where the sulfur dioxide is oxidized to sulfuric acid and titrated with standard alkali.The apparatus consists essentially of a 500-mLthree-neck,round-bottom boiling flask,a separatory funnel having a capacity of 100mLor greater,a gas inlet tube of sufficient length to permit introduction of the carbon dioxide within 2.5cm of the bottom of the boiling flask,a reflux condenser having a jacket length of 200mm,and a delivery tube connecting the upper end of the reflux condenser to the bottom of a receiving test tube.Apply a thin film of stopcock grease to the sealing surfaces of all the joints except the joint between the separatory funnel and the boiling flask,and clamp the joints to ensure tightness.

Procedure— Add 150mLof water to the boiling flask.Close the stopcock of the separatory funnel,and begin the flow of carbon dioxide at a rate of 100±5mLper minute through the Apparatus.Start the condenser coolant flow.Add 10mLof Hydrogen peroxide solutionto a receiving test tube.After 15minutes,without interrupting the flow of carbon dioxide,remove the separatory funnel from the boiling flask,and transfer 25.0g of test specimen into the boiling flask with the aid of 100mLof water.Apply stopcock grease to the outer joint of the separatory funnel,and replace the separatory funnel in the boiling flask.Close the stopcock of the separatory funnel,and add 80mLof 2Nhydrochloric acid to the separatory funnel.Open the stopcock of the separatory funnel to permit the hydrochloric acid solution to flow into the boiling flask,guarding against the escape of sulfur dioxide into the separatory funnel by closing the stopcock before the last few mLof hydrochloric acid drain out.Boil the mixture for 1hour.Remove the receiving test tube,and transfer its contents to a 200-mLwide-necked,conical flask.Rinse the receiving test tube with a small portion of water,add the rinsing to the 200-mLconical flask,and mix.Heat on a water bath for 15minutes,and allow to cool.Add 0.1mLof Bromophenol blue indicator solution,and titrate the contents with 0.1Nsodium hydroxide VSuntil the color changes from yellow to violet-blue,with the color change lasting for at least 20seconds.Perform a blank determination,and make any necessary correction (see Titrimetry á541ñ).Calculate the content,in µg per g,of sulfur dioxide in the test specimen taken by the formula: in which 32.03is the milliequivalent weight of sulfur dioxide;Vis the volume,in mL,of titrant consumed;Nis the normality of the titrant;and Wis the weight,in g,of test specimen taken.NF23