XXIX] DRUGS 363 



(C) Standard nitrite solution. —S^c\g\\ out 0.220 gram of dry silver nitrite [XV, 

 18 (c)], dissolve in a small quantity of hot water and decompose with a slight ex- 

 cess of sodium chlorid solution. When the solution becomes clear, dilute to 1 liter 

 with nitrite-free water. Dilute 5 cc. of this solution to 1 liter with nitrite-free water. 

 The second dilution, containing 0.0001 mg. of nitrous nitrogen per cc, is the stand- 

 ard to be used. [Cf. IV, 12 (d)] 



37 DETERMINATION. 



Place 5 cc. of the ether solution, A or C under 33, in a 50 cc. beaker 

 dilute with 5-10 cc. of alcohol and add about 5 cc. of 0.5% alcoholic potassium hy- 

 droxid. Cover with a watch glass and allow to stand 10 minutes. Place on a steam 

 bath, boil, remove the watch glass and, when most of the liquid has evaporated, add 

 about 25 cc. of water and return to the steam bath until about half the liquid has 

 evaporated or until the odor of alcohol can no longer be detected. Cool and dilute 

 with nitrite-free Avater to 250 cc. Each cc. of this solution represents 0.01 of a 

 tablet. Introduce an aliquot, representing 0.02-0.04 mg. of nitroglycerin, into a 

 100 cc. graduated flask, dilute with sufficient nitrite-free water to make the volume 

 90-95 cc, add a drop of concentrated hydrochloric acid, then 2 cc. of the sulphanilic 

 acid solution and 2 cc. of the alpha-naphthylamin hydrochlorid solution. Com- 

 plete the volume with nitrite-free water. Prepare at the same time and in the same 

 manner standards containing known amounts of sodium nitrite. Stopper the flasks, 

 mix well and compare the colors after 30 minutes, using any convenient colorimeter 

 or Nessler tubes. Multiply the nitrite nitrogen found by the factor 8, which has 

 been determined experimentally, to obtain the equivalent of nitroglycerin. 



When 33 (a) i.s used for the preparation of the sample, a correction, deter- 

 mined as directed above, should be made for the amount of nitroglycerin in B 

 under 33, using all of B instead of an aliquot. 



Pepsin in Liquids.-tentative. 



38 REAGENTS. 



(a) Standard pepsin. — Powder a good grade of U. S. P. pepsin and pass it through 

 a No. 60 sieve; dry in vacuo over calcium chlorid, again pass through a sieve and 

 preserve in a stoppered bottle. Ascertain the exact pepsin equivalent of the dry 

 powder by the U. S. P. method'" and express in percentage based on the assaraptiou 

 that the U. S. P. product is 100% pure. 



(b) Standard pepsin solutions. — Weigh off definite amounts of the standard pep- 

 sin into the requisite quantity of N/10 hydrochloric acid to make solutions con- 

 taining 5 and 0.5 mg. of pepsin per cc. These should be freshly prepared. 



(C) Ricin solulion. — Grind commercial ricin, similar to the "Ricin Prepiirat nach 

 Jacoby", to a No. 60 powder, mix thoroughly, dry and keep in a desiccator. Digest 

 1 gram of this powder for an hour at 37.5°C. in 100 cc. of 5% sodium chlorid solution, 

 cool, filter and use at once for the assay. 



PREPARATION OF SOLUTIONS. 



39 



(a) Dilute solulion of the sample. — Dilute the sample with a measured amount of 

 N/10 hydrochloric acid until, upon digestion at 37.5°C., 1 cc. requires approximately 

 15 minutes to digest the precipitate obtained by mixing 2 cc. of the ricin solution 

 and 0.5 cc. of N/10 h3'drochloric acid. To 50 cc. of this diluted preparation add the 

 requisite quantity of water or of N/5 hj'drochloric acid to make the preparation of 

 N/10 acid strength when diluted with N/10 acid to 90 cc. Preserve the sample in 



