CEETIFICATES AND PAYMENT 159 



also provided that no allegation by the contractors of know- 

 ledge of or acquiescence in deviations or additions on the part 

 of the employers should be accepted or available as equivalent 

 to the engineer's certificate, or in any way supersede the 

 necessity of such certificate as the sole warrant for deviations 

 or additions. While the work was proceeding, the contractors 

 were allowed to erect girders of a heavier weight, inasmuch as 

 they stated that it was impossible to cast girders of the speci- 

 fied weight. The actual weights were entered from time to 

 time in the progress certificates granted by the engineer. 

 When the work was completed, the contractors claimed a sum 

 in excess of the contract price for the extra weight of metal 

 supplied. It was held that the progress certificates were not 

 written orders, and that the claim was therefore excluded by 

 the contracts. 



