82 AGRICULTURAL CHEMISTRY 



and Nad were brought together? (2) Is HC1 a solid, liquid, or 

 gas? Why? (3) Color? (4) Is it soluble in water? Why? (5) 

 What was formed when the HC1 was added to the test-tube con- 

 taining AgNO 3 ? Give the reaction. (6) Is HC1 combustible or a 

 supporter of combustion? (7) What is a chlorid? (8) What 

 effect would HC1 gas have upon plants ? 



87. Properties. Hydrochloric acid is a colorless gas, 

 soluble in water. When exposed to the air, it combines 

 with the moisture of the air. The concentrated acid 

 used in the laboratory is a solution of about 40 per cent. 

 HC1. Chemically, HC1 is an active acid, and is neither 

 combustible nor a supporter of combustion. When it 

 neutralizes bases, chlorids are always formed. Hydro- 

 chloric acid is distinguished from other acids by its reac- 

 tion with silver nitrate, a white precipitate of silver 

 chlorid being produced which is soluble in ammonia and 

 is blackened in sunlight. Hydrochloric acid is used 

 extensively in the laboratory in the preparation of vari- 

 ous compounds, and for the production of chlorin. 



88. Preparation of Chlorin. Chlorin is prepared by 

 the action of an oxidizing agent, as manganese dioxid, 

 upon hydrochloric acid, manganese chlorid, water, and 

 chlorin gas being formed as products. The reaction is 

 MnO 2 + 4HC1 = MnCl 2 + 2H 2 O + 2C1. In this reaction 

 the valence of manganese is changed from 4 to 2, and as 

 a result free chlorin gas is liberated. The method of 

 preparation in the laboratory is as follows : 



Experiment 14. Preparation of chlorin. It is preferable 

 to set up the apparatus for generating chlorin under one of the 

 hoods. Arrange the apparatus as shown in Fig. 41. Place 10 

 grams of MnO 2 and 15 or 20 cc. of HC1 in flask A. By means of 



