SCIENCE— ADVERTISEMENTS 



Freas Constant Temperature Electric Ovens 



FREAS OVEN NO. 100 



A general purpose drying Oven, It has satis- 

 factorily aided many scientists in their work. It 

 may help you. For sale by all dealers. 



Manufactured by 



THE THERMO ELECTRIC INSTRUMENT CO., 



No. 8 Johnson St., Newark, N. J. 



ELECTRICAL MEASURING 

 INSTRUIVIENTS 



FOR PHYSICISTS AND 



PHYSICAL CHEMISTS 



EQUIPMENTS SUITABLE FOR RESEARCH 

 AND INDUSTRIAL LABORATORIES 



Wc Solicit Iiiguiries 



LEEDS &, NORTHRUP CO. 



4901 STENTON AVENUE PHILADELPHIA 



REACTIONS OF SOILS 



May be quickly and accurately determined 

 through use of the 



"LAMOTTE" 

 INDICATOR FIELD SET 



Complete writh instructions. $4.25 (delivered) 



H-Ion concentration of water and (olutioni 



quickly and easily determined by the 



"LAMOTTE" 



H-ION COMPARATOR SET 



Complete and ready for use. $9.10 (delivered) 



SEND FOR UTERATURE 



LaMotte Chemical Products Co. 



Baltimore, Md., U. S. A. 



PRECISION 



Tuning Forks 



Made in wide range of frequency up to 5000 vibrations. Twenty-five years of experience 

 have placed us in position to guarantee absolutely accurate rating. In rating our Forks we 

 use a standard supplied by Dr. D. C. Miller, of the Case School of Applied Science, Cleve- 

 land, Ohio. Our electrically maintained Forks are well known for their convenient mount- 

 ings permitting of great range of adaptability. 



WM. GAERTNER & CO., 



5345-49 Lake Park Ave., Chicago, 111. 



INSTRUCTOR IN ZOOLOGY 

 A man with M.A. or Ph.D. degree want- 

 ed as instructor in Zoology in West Vir- 

 ginia University. Address, Zoology De- 

 partment, Morgantown, West Virginia. 



The Microscope 



By SIMON H. GAGE of Cornell University 



13th Edition, Published December, 1920 



In tliia edition, special emphasis ia put upon the Dark-Field 

 Microscope. POSTPAID $3.00. 



COMSTOCK PUBLISHING CO., Ithaca, N. Y. 



Advertiser, forming Library, wishes to purchase 

 second-hand books on Botany, Biology, Mycol- 

 ogy* Chemistry, Physics, Agriculture, Tech- 

 nology and General Science. State edition and 

 lowest prices to: 

 Mycologist, Mundakayam, Travancore, India 



Chemist, M. S. Wide experience in teaching 

 general analytical, organic and nutritional chem- 

 istry desires position. Prefer research or teach- 

 ing. Good knowledge of animal and plant 

 nutrition. Address: "W," c|o Science, 26 1 9 

 Grand Central Terminal, New York City. 



