26 PROCEEDINGS OP THE AMERICAN ACADEMY 



Marsh method, prescribes that " 440 sq. cm. of the article ... by 

 reductiou with potassic cyauide and sodic carbonate, shall not produce 

 more than a partially opaque mirror in a glass tube of 1.5 to 2 mm. 

 inner diameter." Thoms * in 1883 proposes as a means of control 

 that the results from 100 sq. cm. of paper should be divided into 

 four grades : " strongly arsenical,"' " arsenical," " traces," and " free." 

 If, when the apparatus has been running ten minutes after the intro- 

 duction of the solution to be tested, a deposit is obtained no larger 

 than that corresponding to what is produced by 0.1 mgr. of arsenious 

 oxide under similar conditions, the paper may be considered to con- 

 tain a " trace," and need not be rejected. 



A committee of the National Health Association of Great Britain, 

 consisting of Messrs. Bartlett, Heisch, and De Chaumout,! suggested, 

 in 1883, that a paper should be considered non-arsenical if, after being 

 treated by a modification of the Berzelius-Marsh method devised by 

 them, it failed to give a mirror in a tube of one eighth inch internal 

 diameter (about 3.3 mm.) sufficient to cut off at any point a black line 

 of a certain thickness (" thick rule, 8 to pica ") on a white ground. 



All this is very crude, yet, without a means of easily estimating 

 the amount of arsenic present, it might answer until the exact de- 

 termination was called for. 



The length of time necessary for any of the quantitative methods 

 precludes their use by analysts, especially when, as is generally the 

 case, the quantitative determination is not of especial importance. 

 If we attempt to apply the gravimetric Berzelius-Marsh method to 

 the analysis of wall paper, we are met, not only by the amount of 

 time necessary for the complete deposition of the arsenic mirror, 

 but by the large amount of paper that must be taken, or, if the 

 proportion of arsenic is very small, the unwieldy amount. Added 

 to this is the necessity for a delicate balance, and also the error in 

 weishinff small mirrors of arsenic. 



A method is therefore desirable which will allow us to estimate 

 minimal amounts of arsenic, and, in such analyses as that of wall 

 paper, will give an approximate idea of the amount present without 

 requiring more time than that needed for the proper -conduct of the 

 ordinary Berzelius-Marsh method. 



The process which is described in the following pages was sug- 

 gested by Professor H. B. Hill of Cambridge, about five years ago, 



* Ref. Fres. Zeitschr., XXII. 474, from Ber. d. landw. chem. Vers. u. Samen- 

 controlstat. zu Riga, 1883. 

 t Brit. Med. Jour., 1883, p. 1218. 



