NITROGEN-BONDED RADICALS: IDENTIFICATION 



on the cavity slide and put on it, over the fringencc, dichroism if it occurs (as with 

 center of the cavity, a little droplet of sodium diethylamine hioniaurate), etc., as well as 

 tetraphenylboron solution (1:20 in water); form. To the case of the red and brownish- 

 then invert this slide. Tetraphenylboron is yellow hexafi;onal crystals with dimethyl- 

 extremely sensitive to ammonia and the amine (as well as the similar crystals, 

 lower amines, and if one of them is evolved, brownish -yellow only, with methylethyl- 

 characteristic crystals form rapidly in the amine) it is surprisingly easy to get a good 

 hanging drop. Examine them with a polariz- interference figure (a uniaxial cross), and 

 ing microscope with the slide in place, or determine the sign of the crystal (positive), 

 transferred over an empty cavity to prevent Working sensitivities, except for reagent 

 further formation. In case of a mere trace of 3, are of the order of hundredths of a micro- 

 ammonia, compare with a blank test using gram of the evolved amine captured in the 

 the same reagents. Ammonia is so common hanging drop. Reagent 3, although less sen- 

 from various causes, including contamina- sitive than was desired, can be vised for 

 tion, and the tests so sensitive, that often highly characteristic crystals with as little 

 its crystals are not very distinctive, as those as 4 or 5 micrograms of ethylamine. The 

 of the lower amines are. alternative given for ethylamine, reagent 4, 



Usually a result appears within a few min- has the desired sensitivity, but has disadvan- 



utes, if at all. If there is no result in an hour tages due to the reagent itself, and because 



or so, add a drop of 1 % KMn04 solution and the crystals of the particular test are less eas- 



invert over the cavity a fresh droplet of ily distinguishable from others than is the 



tetraphenylboron solution. Or better, if case with the other recommended tests. The 



there is no shortage of material, run the test tests with reagent 5 can be obtained in the 



with oxidation at the same time as the one presence with NH4CI. (See table), 



with alkali alone. The oxidation test may Compare results closely with the crystals 



give a different result even when there is given by knowns, until ciuite familiar with 



some evolution of a volatile base. Examine them. 



the crystals wdth the slide still inverted, over Selection of a "best test" for ethylamine 



an empty cavity. gave the most difficulty. Its test with 



If either technique is effective for crystals IIAuBr4 in 2H-iP04- IHBr was passed over at 

 apparently due to a lower amine, prepare the time the table was drawn up, because 

 another test. Use a hanging drop of simply good crystals form only at the periphery of 

 1 % of concentrated HCl in water. After an precipitation. However, they are very char- 

 exposure which may be judged from the acteristic, divided hexagons, quite different 

 previous reaction, or up to about an hour, from the crystals of methylamine (or any 

 reinvert the slide and allow the drop to dry others so far seen) with this reagent. HAuBr4 

 up (it may be put in a desiccator if hygro- in 2H3P04-1 (Acetic acid) also gives good re- 

 scopic). Examine the residue with a polariz- suits. These tests may be compared with the 

 ing microscope and then test with one of the tw^o that had been selected for the table, 

 reagents suggested below, according to the Various examples of microcrystals of com- 

 identification or indication of the tetraphen- pounds are illustrated in Fig. 1 for NH? , and 

 ylboron test. Fig. 2 for methyl-, ethyl-, dimethyl- and tri- 



Put a droplet of reagent on a small cover- methylamines. 



glass, then invert it upon the residue of hy- Test for Aninioiiia with Formalde- 



drochloride. Examine the crystals, using a hyde. There should be no difficulty in iden- 



polarizing microscope, with magnifications tifying ammonia with certainty in the fore- 



of about 100 X and 200 X, observing bire- going procedure, noting the small crystals 



47 



