PAPERS ON CHEMISTRY AND PHYSICS 297 



sprayed with the solution of ammonium thioeyanate and 

 dried. It is a negative test producing a red stain on the 

 untreated portion and not affecting the color of the 

 treated portion. The red stain is ferric sulphocyanate, 

 which is attacked by the phosphates in the wood and de- 

 composed, leaving the natural wood color. 



It was found that ferrous salts in an acid solution used 

 in conjunction with ammonium thioeyanate solution pro- 

 duced a good test, but it was not permanent. It faded in 

 a few hours. The method used was the same as that used 

 above except that the solutions were made with water. 

 The wood was sprayed first witli a solution of ferrous 

 ammonium sulphate and then dried. It was then sprayed 

 with a solution of ammonium thioeyanate. The resulting 

 color was red on the untreated parts and natural color 

 on the treated parts. 



As the water solutions of ferric salts are turned black 

 by tannic acid, it is impossible to use them on any wood 

 containing an appreciable amount of tannic acid. The 

 method used on woods that did. not contain tannic acid 

 was the same as the above except that ferric chloride was 

 substituted for ferrous ammonium sulphate. This test 

 gave a good red Main on the untreated parts and did not 

 affect the color of the wood that was treated. It lacked 

 permanence as did the others. 



The test that was found to be the most satisfactory in 

 the laboratory was the one using the water solutions of 

 potassium ferricyanide and iron ammonium chloride. 

 First, the surface of the wood to be tested is sprayed 

 with a five per cent solution of potassium ferricyanide 

 and dried. Then it is sprayed with a five per cent solu- 

 tion of iron ammonium chloride, and as soon as the line 

 dividing the treated and the untreated portions appears 

 the surface of the wood is washed thoroughly with tap 

 water. The test should be performed in ordinary day- 

 light, not direct sunlight. The untreated part of the 

 wood is colored a deep blue and the color of the treated 

 portion is not changed. It generally takes about three 

 or four seconds for the line to appear, and the test works 

 equally well on pine, oak, or fir woods with widely di- 

 vergent qualities. 



