Responsa for Bava Kamma 230:2
שטף נחל חמורו וחמור חבירו שלו יפה מנה ושל חבירו מאתים והניח זה את שלו והציל את של חבירו אין לו אלא שכרו ואם אמר לו אני אציל את שלך ואתה נותן לי את שלי חייב ליתן לו:
AND HE LEFT HIS OWN ASS [TO ITS FATE], AND RESCUED THE OTHER MAN'S ASS, HE WOULD BE ABLE TO CLAIM NO MORE THAN THE VALUE OF HIS SERVICES; BUT IF HE SAID TO HIM [AT THE OUTSET], 'I AM GOING TO RESCUE YOUR ASS AND I EXPECT TO BE PAID AT LEAST THE VALUE OF MY ASS,' THE OTHER WOULD HAVE TO PAY HIM [ACCORDINGLY]. <b><i>GEMARA</i></b>. But why [should the rescuer] not be entitled to say, 'I have acquired title to the rescued object<span class="x" onmousemove="('comment',' I.e., the honey by receiving it in my receptacle. ');"><sup>3</sup></span> as it became ownerless'?<span class="x" onmousemove="('comment',' For when the jug cracked and the loss of the honey became imminent there is implied Renunciation on the part of the owner; v. also supra p. 670 and B.M. 22a. ');"><sup>4</sup></span>
Teshuvot Maharam
A. A dowry gift becomes the property of the donee only if the marriage takes place. Therefore, neither A nor his daughter has ever gained title to B's money, and A must return the principal plus the interest to B. Even if B expressly stipulated that he will forfeit the 15 pounds if the marriage does not take place, such a stipulation is considered an Asmakhta and is not valid. B, however, must pay A for his trouble in managing B's investments.
SOURCES: Cr. 86; Pr. 285; Mord. B.B. 615; Agudah B.B. 198.
Teshuvot Maharam
A. Throughout the kingdom, Rashi's view is accepted that a Humash is not an object that is usually borrowed or hired. B therefore may take an oath that the book was pledged with him for two marks. However, B should be careful in taking his oath; for, if A did not actually owe him two marks, but promised to give B two marks if the latter effect a reconciliation between A and his son, A became indebted to B only for the latter's wages for the time and effort expended, but not for full two marks.
SOURCES: Pr. 1007.