CHEMISTRY. 



101 



detectable by it : thus the l-100,000th or even the 

 l<d|000,000tb part of a grain of arsenious acid, dis- 

 i in tin- same quantity of water (I <-.<.. will 

 att'"rl, by the blackening of the silver salt, at't i a 

 little time, an indication of the presence of arsenic. 

 Nor in thin method of detecting arsenic directly ap- 

 plh-alilu only where it exists as arsenious acid, but 

 likewise to several other compounds of arsenic, 

 whether they are soluble or insoluble in water; 

 thus, for example, the two sulphides of arsenic 

 (orpimeiit and realgar), the alkaline arseniates, and 

 even metallic arsenic itself if reduced to powder, 

 will readily show their arsenical nature oy this 

 test ; and we may in a few moments detect by it the 

 occurrence of arsenic in different green, yellow, and 

 orange pigments, which are still much employed in 

 the manufacture of wall-papers, in painting, and in 

 the coloring of certain textile and other articles used 

 in dress or for ornamentation. 



Distribution of Arsenic in the Tissues. 

 This subject baa been reinvestigated by Sca- 

 losuboff, who experimented on dogs, rabbits, 

 and frogs. The poison was administered with 

 the food, in the form of arsenite of soda. It was 

 afterward separated from the tissues by treat- 

 ing these with a mixture of nitric and sul- 

 phuric acids, evaporating nearly to dryness, 

 adding more sulphuric acid, heating again till 

 fames appeared, and then, after adding more 

 nitric acid, heating to carbonization. -On ex- 

 haustion, with boiling water and filtering, a 

 liquid is obtained, from which the arsenic may 

 be precipitated by sulphureted hydrogen. It 

 was found that dogs bear large doses of arsenic 

 well, taking, without difficulty, fifteen to eigh- 

 teen times the quantity, which, weight for 

 weight, would kill a man. Arsenic was fed 

 to a bull-dog for 84 days, the quantity being 

 gradually increased from 5 to 150 milligrammes 

 per day : 1 00 grammes of the muscle of this 

 dog contained .00025 gramme arsenic, 100 

 grammes of liver .00271 gramme arsenic, 100 

 grammes of brain .00885 gramme arsenic, 

 and 100 grammes of spinal cord .00933 gramme 

 arsenic. Calling the quantity in 100 grammes 

 of muscle 1, that in the same weight of liver 

 is 10.8, brain 3(5.5, and spinal cord 37.3, thus 

 showing the marked tendency of the arsenic 

 to localize itself in the nervous tissues. 



Ammonia as a Chemical Impurity. An im- 

 portant contribution to the subject of the 

 purity of chemicals has been made by Prof. F. 

 H. Storer, in an account of his investigations 

 (American Journal of Science and Arts) con- 

 cerning the presence of ammonia as a contam- 

 inant of sulphuric acid, and of those substances 

 in the manufacture of which sulphuric acid is 

 employed. SchSnbein stated in 1862 that am- 

 monia was found in all the samples of sulphu- 

 ric acid he had tested for its presence. Prof. 

 Storer's results are equally conclusive, nine 

 samples from different sources which he ex- 

 amined showing the presence of this impurity 

 In appreciable quantities. 



" There are several ways," says Prof. Storer, 

 " in which sulphuric acid may be contaminat- 

 ed with ammonia. Some insignificant traces 

 of this substance are, of course, contained in 

 the air which is used for making the acid, and 



a still larger amount is often contained in tb 

 water that playa so important a part in the 

 process of manufacture. It is not impossible, 

 indeed, that nitrogen compounds in the water 

 may sometimes be the cause of appreciable 

 traces of ammonia in the acid. It is easy to 

 conceive, moreover, that considerable quan- 

 tities of ammonia may be formed in the ap- 

 paratus of the sulphuric-acid maker through 

 reduction of nitric acid, or other oxide of 

 nitrogen, that is necessarily present; and I 

 find, in fact, by direct experiment, that am- 

 monia is formed when warm dilute nitric acid 

 is made to act upon lead or upon sulphur. 



'' A quantity of soft, clean, commercial lead 

 that had just been remelted was placed in a 

 small glass flask and 50 c.c. of dilute nitric 

 acid (sp. gr. 1.15) were poured upon it. The 

 flask was closed against the air with a gas- 

 delivery tube, and after the action of the acid 

 had ceased the solution was boiled with the 

 milk of lime, and the distillate tested for am- 

 monia. But the reaction with Nessler's liquor 

 was so strong that no estimation of the amount 

 of ammonia could be made. A quantity of 

 the lead (30 grammes), boiled by itself in the 

 milk of lime, gave a distillate in which no am- 

 monia could be detected by the Nessler test. 

 On the other hand, 50 c.c. of the dilute nitrio 

 acid were found to contain 0.000025 gramme 

 of ammonia. 



" In a second trial, 50 grammes of the com- 

 mercial lead were wanned during three hours 

 with 50 c.c. of the dilute nitric acid. The so- 

 lution was distilled with the milk of lime, and 

 the ammonia in the distillate was estimated by 

 titration with standard oxalic acid : 0.002483 

 gramme of ammonia was found. 



" In a third trial 25 grammes of pure lead 

 (from Marquart, of Bonn) were warmed with 

 50 c.c. of the dilute nitric acid, and 0.003279 

 gramme of ammonia was found in the solution 

 of nitrate of lead. 



" Fifteen grammes of clean copper clippings 

 were gently warmed with 50 c.c. of the dilute 

 nitric acid until there was no more action. 

 The solution was distilled with milk of lime, 

 and the ammonia estimated by Nessler's test: 

 0.00004 gramme of ammonia was found. 



"Twenty grammes of powdered brimstone 

 were added to 50 c.c. of the dilute nitric acid, 

 and the mixture was maintained at or near the 

 temperature of boiling for three hours. On 

 testing the liquid an abundance of ammonia 

 was found. 



"In another trial, 20 grammes of the pow- 

 dered brimstone were mixed with 100 c.c. 

 of the dilute nitric acid. The mixture was al- 

 lowed to stand in the cold for 48 hours, and 

 then boiled gently during 8 hours. On test- 

 ing the liquor by the Nessler process 0.00225 

 gramme of ammonia was found in it. 



" A small amount of nitrogen oxides may 

 perhaps be reduced to ammonia in the process 

 of sulphuric-acid making by other deoxidizing 

 agents, such as the organic imparities of crude 



