82 THE LAW AFFECTING ENGINEERS 



far the contractor can make a claim for extras or seek to go 

 behind the terms of the contract. Indeed, it may be said that 

 amongst the causes of dispute which arise in relation to 

 engineering there is none more fruitful than the question of 

 extras and deviations. 



Without going at any length into the question of extras 

 (which will be found fully dealt with in the chapter on extras, 

 Chap. XII., post) it may be stated generally that if the con- 

 tractor has undertaken to do work for a specific sum, on the 

 terms that extras are only to be ordered by the engineer, he 

 cannot recover anything in respect of extras unless he has 

 obtained the necessary order. Thus the contract often con- 

 tains a provision enabling the plans and specifications to be 

 modified by the employer through the engineer, and protecting 

 the employer from any claim for extras unless the contractor 

 has obtained an alteration order from the engineer and has 

 complied with a number of conditions as to notices, measure- 

 ments, certificates, etc. 



29. Impracticability of the works. The fact that the 

 scheme which he has undertaken is impracticable or that 

 there are unforeseen difficulties in the way of the contractor 

 affords him no excuse for renouncing his contract or making 

 any claim for extra payment. A carefully drawn contract 

 always provides that the employer does not guarantee the 

 practicability of the scheme which it is designed to put into 

 execution ; but even in the absence of such a clause, the 

 contractor can set up no usage or custom to the effect that the 

 employer warrants the practicability of the scheme (see 15 (c), 

 ante). The conditions of a large contract generally contain 

 a clause specially warning the contractor to make proper 

 investigations for himself (see sub-tit. " Statement of condi- 

 tions to be observed on tendering," Chap. VIII., 8, post ; and 

 Form IIA., Cls. 9 and 9A>. 



30. New contract arising out of an old contract. Where 

 there is a contract to erect buildings or carry out works on 

 certain terms, and this contract is allowed to lapse, but the 

 employer then encourages the contractor to do the work, the 

 contractor may sue as upon an implied contract. Thus in 

 Burn v. Miller, 1813, 4 Taunt. 745, a landlord contracted to 

 pay his tenant at a valuation for certain erections pursuant to 



