1850 Journal of Applied Microscopy 



water 160 c. c). Mix thoroughly and centrifuge it for three minutes at a speed 

 of 1000 revolutions per minute. The percentage indicated on the tube will be 

 8 per cent., that is, a little below the mark 1 on the tube. 



The sulphates are increased in febrile diseases, especially in acute rheuma- 

 tism, pneumonia, diabetis mellitus and leukaemia. They are decreased in chronic 

 diseases of the kidneys. William H. Knap. 



Harvey Medical College. 



MICRO-CHEMICAL ANALYSIS. 

 XX. 



SILVER GROUP CONTINUED— LEAD. 



This element is found in the 10th series of Group IV of the Periodic System. 

 The other basigen in this group which we will consider is tin. Between tin and 

 lead there is an, as yet, undiscovered element. On account of this serious gap 

 it is simpler to discuss the micro-chemical reactions of lead in connection with 

 silver than to attempt to do so with tin. 



Lead can be satisfactorily detected in the presence of other elements by 

 several reagents, the most important of these being : 



I. Hydrochloric Acid. 

 II. Sulphuric Acid. 



III. Potassium Iodide. 



IV. Ammonium Bichromate. 



V. Copper Acetate with Potassium Nitrite. 



Of these reagents the analyst will generally select, for ordinary work, either 

 III or V. But he will usually have already noted the effect of hydrochloric or 

 sulphuric acids in either dissolving the substance or in applying a general group 

 test. 



The analyst must ever bear in mind the tendency on the part of lead to form 

 basic salts and double salts. The former because of their insolubility often 

 appearing as more or less amorphous precipitates and the latter frequently sepa- 

 rating when least expected as beautifully crystallized compounds when other 

 elements are being tested for. 



In testing alloys practically the only solvent available is nitric acid. But 

 when using nitric acid it must be remembered that lead nitrate is a salt of rather 

 low solubility and that it is far less soluble in nitric acid than in water. If con- 

 centrated nitric acid has been employed for attacking the substance it follows 

 that very little lead will have passed into solution. Lead nitrate crystallizes in 

 beautiful clear cut transparent octahedra and the usual combinations of the 

 isometric system. The worker in micro-chemical analysis should familiarize 

 himself with the appearance and peculiarities of this salt in order to take advan- 

 tage of its chance separation, which will enable him to remove the greater part 

 of the lead which may be present and to obtain a pure salt upon which to work. 



