The following opinion was filed June 6, 1922:

It is conceded that at no time prior to the delivery of the fan was appellant’s attention called to the fact that it was to be used in connection with the operation *184of four 100 horse-power boilers. There is no dispute on the part of the experts testifying in the case that the capacity of the fan is to be measured by the number of cubic feet of gases per minute which it can handle; that the size of a fan required to permit the simultaneous operation of at least three of the boilers at 200 per cent, rating is an engineering problem, and that in order to design a fan to accomplish such result it is necessary to know the size of the boilers. Appellant contends that because the specifications for the fan were silent with respect to the size of the boilers, but did require a maximum capacity of at least 20,000 cubic feet of gases per minute, it was justified in assuming that the engineer who prepared the specifications had figured out the necessary capacity of the fan to be 20,000 cubic feet of gases per minute. We see no escape from this conclusion. There is nothing from which an intent on the part of respondents that appellant should solve the engineering problem of the required capacity of a fan necessary to produce the simultaneous operation of at least three of the boilers at 200 per cent, rating can be inferred. To solve this problem without any knowledge concerning the size of 'the boilers is an engineering impossibility. Appellant, it seems, was entirely warranted in believing that the engineer preparing the specifications had figured that a fan having a maximum capacity of at least 20,000 cubic feet of gases per minute was of sufficient capacity to permit the simultaneous operation of at least three of the boilers at 200 per cent, rating, and that it was no part of its duty to figure on the capacity of the fan required.

It being conceded that the fan had a maximum capacity of at least 20,000 cubic feet of gases per minute, it complied with the warranty and there is no basis for respondents’ counterclaim. It is true that appellant attempted to remedy the fan so as to develop the required capacity, which attempt was also a failure. Its efforts in this behalf, however, were gratuitous and can form no basis for liability. The liability, *185if any, must be predicated upon the original agreement and warranty.

Appellant also complains because the trial court did not allow interest on the book account from the date of the last entry. The brief contains a statement that it is fundamental that a book account draws interest from the date of the last entry. Such is not our understanding of the law. A book account draws interest only from the date of demand of payment, and in this case there was no proof of a demand prior to the commencement of the action. Interest, therefore, can be allowed only from that time. Marsh v. Fraser, 37 Wis. 149.

By the Court. — Judgment reversed, and cause remanded with instructions to dismiss the counterclaim and render judgment in favor of the plaintiff for the amount of the book account with interest thereon from the date of the commencement of the action.

A motion for a rehearing was denied, with $25 costs, on October 10, 1922.