192 EESEARCHES UPON THE CHEMICAL PROPERTIES OP GASES. 



slow, the reaction is extremely delicate. It is accelerated by warming to 100°. 

 Minute quantities of carbon monoxide in air may be recognized by the precipitation 

 of metallic palladium from palladium chloride solution. The precipitation often 

 appears in the form of a lustrous metallic film of dark brown color coating the glass. 

 My experiments upon the action of olefines show, however, that it is essential to the 

 identification of carbon monoxide that the formation of carbon dioxide by the action 

 of the palladium chloride be proved by means of lime water or other indicator, as 

 otherwise the reduction of the palladium salt may be due to a member of the define 

 group. The air may be caused to flow slowly through palladium chloride solution 

 and then into lime water. The tendency to undergo oxidation to carbon dioxide on 

 the part of carbon monoxide, and the absence of such tendency on the part of the 

 olefines when exposed to oxidizing influences at a temperature of 100° or below, 

 serves as a most important criterion for the purpose of distinguishing between CO 

 and the define group. Winkler {Fres. Zeit, 1889, p. 269) has called attention to 

 the value of palladium chloride as a reagent for the detection of carbon monoxide 

 and has made many valuable suggestions. (For a very convenient form of apparatus 

 for the quantitative determination of carbon monoxide by palladium chloride, see 

 Ellen Richards, Am. CTiem. Jour., Yd. Yll.) 



Platinum chloride is also a valuable reagent for the detection of carbon monox- 

 ide. Although oxidation to carbon dioxide occurs, no metal is precipitated unless 

 the exposure to the gas be continued for several days, when traces of platinum 

 appear. The solution assumes a darker color and a partial reduction results. 



Gold chloride solution is as energetic as palladium chloride in causing oxidation 

 of carbon monoxide. 



The reduction of ammoniacal nitrate of silver solution by carbon monoxide has 

 been described by Berthelot ( (7o?np<. Rend., CXII, p. 597). Although chromic acid 

 produces minute traces of carbon dioxide at 100° when carbon monoxide is conducted 

 through its solution, my results do not confirm the statements of Ludwig (^Ann. Ch. 

 Pharm., CLXIl, p. 47), according to whom carbon monoxide may be determined by 

 oxidation to carbon dioxide caused by chromic acid solution. 



The interesting compound formed by the direct union of carbon monoxide and 

 platinum chloride (Pullinger, J. Oh. Soc, 1891, p. 598) is not likely to prove of 

 importance in connection with the study of gas reactions. 



Among the reactions I have studied, the most important for distinguishing be- 

 tween olefines and carbon monoxide are the fdlowins: : 



(1) The action of palladium chloride, which in the case of carbon monoxide 



